Washability of e-textiles: current testing practices and the need for standardization

Abstract

Washability is seen as one of the main obstacles that stands in the way of a wider market success of e-textile products. So far, there are no standardized methods for wash testing of e-textiles and no protocols to comparably assess the washability of tested products. Thus, different e-textiles that are deemed equally washable by their developers might present with very different ranges of reliability after repeated washing. This paper presents research into current test practices in the absence of e-textile-specific standards. Different testing methods are compared and evaluated and the need for standardized testing, giving e-textile developers the tools to comparably communicate and evaluate their products’ washability, is emphasized.

Keywords

e-textiles smart textiles wash testing washability reliability standardization

Textile-integrated conductive materials or electronics, also referred to as smart textiles or e-textiles, are a rapidly growing class of products. These hybrid e-textiles can be characterized as textile products with additional functionality provided by the electronic or electrically conductive components. Examples of these added functions are sensors, lighting, heating, stimulation, or recording of internal or external parameters. Simultaneously, e-textiles constitute electronic products with additional—textile typical—requirements, resulting from integration into a textile base. This is especially true for wearable e-textiles, products that are designed to be worn on or close to the body. To ensure wearer well-being, they need to be sufficiently breathable and comfortable.¹ Textile typical usability also requires an e-textile to be flexible and—depending on the application—stretchable enough to withstand a range of mechanical stresses during use—mainly tensile, but also bending, shear, torsion, or compression stress.² Just as textiles without integrated systems, wearable e-textiles can become stained during their use and therefore need to be cleanable or washable.³ During the washing process, characterized by the four interdependent factors of time/duration, mechanical action, temperature, and chemistry/biology, also labeled Sinner’s factors,¹,⁴ different strain scenarios occur that the e-textile needs to be able to withstand. Especially with a large fraction of e-textile products developed for medical, personal protective equipment (PPE), and sports applications, resulting hygiene requirements make washability an essential property.⁵ E-textiles should hold up to a (use-oriented) type and number of (household) washing cycles during their life cycles, or, in the case of medical or PPE products, even industrial washing if applicable.⁶ From the viewpoint of experts and researchers that work on smart or e-textiles, washability (or a lack thereof) represents a key factor in the lack of commercially successful products.¹,⁵

The need for integrated conductive and electronic components to exhibit a level of washability comparable to their textile substrates also arises from a growing demand for more sustainability. The production of a cotton or polyester shirt alone entails about 4 kg of CO_2.⁷ This impact from the textile base is further increased by the integrated electronic or conductive components. Thus, from a sustainability viewpoint, great care has to be taken to keep the system functioning and in use for as long as possible, reducing the need for replacement. For cyclically used textiles—a use phase followed by a cleaning process that restores the product’s serviceability—this need for an extended lifetime requires the product to be as robust as possible to the strain resulting from the washing or cleaning processes. The complex composition of e-textiles makes this much more challenging than for textile-only products, because all components, with their very different vulnerabilities, have to withstand the cleaning process.⁸

To assess, improve, and evaluate the extent of an e-textile’s reliability when subjected to repeated washing procedures, test cycles have to be run. A reliable comparability of different e-textiles’ washability—important, among other things, to communicate to consumers—is only possible if this testing is done under defined circumstances following similar or even standardized protocols. So far, no proper standards exist that allow for such comparisons. In the absence of e-textile-specific washing standards, test protocols from adjacent fields, in more or less modified form—textile standards being the most common—are used to assess the washability. Or, in lieu of standardized methods, individually designed test protocols are applied to appraise washability.⁶ Because of this great variability of methods, comparability of different test results is low/limited. In many cases, the tested products are deemed washable, even though they exhibit poor fastness to washing procedures.⁸ Some sources even claim washability with no (apparent) prior testing.⁹,¹⁰

This article aims at gaining insight into and analyzing current wash testing practices for smart and e-textiles. A short overview of existing standards for e-textiles precedes a review of scientific publications featuring wash testing of e-textiles. The information about the particular test practices given in the reviewed sources is often incomplete. This can be attributed to wash testing not being the central matter of most publications, but rather one of several reliability tests run to assess a newly developed product or technology—often the main focus of the reviewed publications.

Current situation in standardization

The number of existing standards especially conceived for hybrid e-textiles to date is very low. Of the existing ones, most cover either terminology and/or definitions like ISO/PRF TR 23383 and ASTM D 8248:2020. Others give test methods for resistance measurement of textile-based products: AATCC 76 for fabrics, AATCC 84 for yarns, and CSN EN 16812 for conductive tracks on textiles (see Table 1). IPC-8921 provides terms and definitions, as well as a method for testing the resistance of conductive textile materials. There are current efforts to overcome this lack of e-textile-specific standardization, though. Several other standards are anticipated to be finalized within the next few years (some examples are given in Table 1). These are expected to improve the situation by covering a wider range of issues, including reliability and washability (like IPC 9881 and IEC 63203 204-1).

Table 1.

Existing, upcoming, and external standards for e-textiles

Identification	Title	Year
Existing standards
DS/CEN/TR 16298	Textiles and textile products—smart (intelligent) textiles—definitions, categorization, applications and standardization needs	2012
ASTM D 8248	Standard terminology for smart textiles	2020
AATCC 76	Test method for electrical surface resistivity of fabrics	2018
AATCC 84	Test method for electrical resistance of yarns	2018
CSN EN 16812	Textiles and textile products—electrically conductive textiles—determination of the linear electrical resistance of conductive tracks	2016
IPC-8921	Requirements for woven and knitted electronic textiles (e-textiles) integrated with conductive fibers, conductive yarns and/or wires	2019
Upcoming standards
IEC 63203 204-1	Wearable electronic devices and technologies: electronic textile—washable durability test method for leisure and sportswear e-textile system	2022
IPC 8981	Quality and reliability of e-textiles wearables	2022
IPC 8952	Design standard for printed electronics on coated or treated textiles and e-textiles	?
IPC 8941	Guideline on connections for e-textiles	?

Standards from other fields used in e-textile wash testing
ISO 6330	Textiles—domestic washing and drying procedures for textile testing	2012
ISO 105-C01	Textiles—tests for color fastness—Part C01: color fastness to washing	1989
ISO 15797	Textiles—industrial washing and finishing procedures for testing of workwear	2017
DIN 54015	Testing for colorfastness of textiles—determination of color fastness of dyeings and prints to washing in presence of peroxide	2017
AATCC 6	Colorfastness to acids and alkalis	2016
AATCC 61	Colorfastness to laundering: accelerated	2013
AATCC 135	Dimensional changes of fabrics after home laundering	2018

The most commonly used standard from adjacent fields when testing the washability of e-textiles is ISO 6330 Textiles—domestic washing and drying procedures for textile testing.⁶ Within this standard, a range of household washing and drying procedures are given, reflecting the variety of actual household washing programs. The standard provides testing conditions and instructions for the three most common types of washing machines: horizontal-drum front-loading machines, predominant in Europe, and agitator or impeller type vertical-drum top-loading machines found mainly in America and Asia, respectively.¹¹ The scope of the standard includes not only textiles, but also “other textile articles”—a term that can be applied to hybrid smart or e-textiles—allowing for the standard to be extended for their testing. Not included in the standard are guidelines or recommendations concerning the number of wash cycles that should be conducted nor criteria on how washing reliability can be assessed after testing. Other less often applied standards include ISO 105-C01:1989 Textiles: tests for color fastness—part C01: color fastness to washing, ISO 15797:2017 Textiles: industrial washing and finishing procedures for testing of workwear, and AATCC 61 Colorfastness to laundering: accelerated.

Although presently not (yet) used for e-textile testing, another standard worth mentioning is IEC 60456:2010 Clothes washing machines for household use—methods for measuring the performance. This standard’s scope is not textile wash testing, but the evaluation of washing machines. Included are testing protocols for household washing programs cotton, easy care, and wool. In contrast to the widely used ISO 6330, cleaning capability is assessed and the range for the wash load ranges from 2 to 10 kg. Due to their relative harshness, the applicability of the cotton and easy care washing procedures featured in IEC 60456 for e-textile wash testing would have to be evaluated.

Washability test practices

A literature review of publications about e-textile development or reliability has been carried out to evaluate current wash testing protocols for e-textiles. A total of 73 publications that include a section on wash testing have been selected to serve as a basis for this analysis. Although extensive, this selection is not an exhaustive representation of e-textile wash testing. Since the focus of this article is to evaluate the current testing situation, only research published in 2010 or later has been considered. The reviewed sources have been clustered into four groups according to the employed test practices (due to extensive testing with different methods, two sources have been included in both the household and alternative methods cluster):

wash testing according to ISO 6330 (31 publications);

wash testing according to other standards (13 publications);

wash testing under household washing conditions (19 publications);

wash testing with alternative test methods (12 publications).

The assessment of washability depends on the intended application of the tested product as well as its projected frequency of cleaning and total number of cleaning cycles during its lifetime.⁶ Underwear or sports clothing, products that will be washed after (almost) every use phase—and under sufficiently harsh conditions to ensure hygiene requirements are met—need to be much more robust to washing-related strain than a jacket that will only be cleaned once or twice per year. To determine if and how product types influence the washability test practices for e-textiles, the type of tested product is included in the analysis.

This evaluation of e-textile wash testing practices does not include testing performed by e-textile producers. Those test practices could differ from the surveyed literature sources, but are rarely disclosed to the public.

Testing according to ISO 6330

The following section gives an overview of 31 publications that include wash testing of e-textiles according to ISO 6330,¹,^12–41 (Table 2). From the sources that state the standard version used, 16 follow the newest 2012 version, and 11 the previous 2000 version.

According to ISO 6330, the test vehicles should be washed in a standard-compliant washing machine (vertical or horizontal axis). For a total of 2 kg, additional base load (cotton, cotton–polyester blend, or polyester, depending on the textile material of the test vehicles) has to be added to the machine. The test vehicles should not account for more than half of the total load. One of six standardized detergents, the amount varying with the type of machine and detergent used, has to be added to the machine and one of various given wash programs—differing in their harshness—has to be run. Table 3 shows the ranges of the washing factors for each of the machine types. Afterwards, the test vehicles should be subjected to one of six given drying methods.¹¹ Further instructions are given as to how the test vehicles should be prepared and conditioned, as well as specifications for the water hardness. Neither the number of wash cycles nor a method to evaluate the washability of the tested samples are provided by the standard.

Table 2.

Wash testing according to ISO 6330^a

Source	Version	Tested product	Parameter^b	Washing device^c	Cycles	Load^d	Temperature [°C]	Program/duration [min]^e	Detergent	Drying
Ankhili et al.¹²	2012	ECG electrodes	R, c	Datacolor Ahiba	50		40	30
Baribina et al.¹³	2012	Conductive yarn	R		10	Protective bag	30	3M/23		Air
Blecha et al.¹⁴	2012	Fire-fighter suit	f	HH front	30		60
Erdem et al.¹⁵	2000	Knee pad	R		10		40	4M/25		Air
Foerster¹⁶	2000	Conductive yarn	R	Wascator	20		40	4M/25	ECE-2
Gerhold¹⁷	2000	Textile circuit board, LED module	R	Wascator	16	Protective bag + 2 kg towels	40	4M/25	66 g ECE 105	Air
Hardy et al.¹⁸	2012	Conductive yarn	f	Wascator?	25	Total 2 kg,+CO T-shirts	40	4N/31	20 g Persil	Air, dryer
Huang et al.¹⁹	2012	Conductive paste and yarn	R	Datacolor Ahiba	10		30	30		Air
Kayacan et al.²⁰	2012	Conductive yarn	R	HH	5		40		With
Kazani et al.²¹	2000	Conductive paste	R		20		40	4M/25
Kazani et al.²²	2000	Printed antenna	c	Reference	20		30	3G/16	20 g ECE	Air, 50°C
Kim and Lee²³		Conductive ink	R, c	HH top	20		20	(11B?)/15	5 g/l
Kivanc and Bahadir²⁴	2012	Conductive yarn	R	HH front	5	Total 3 kg	40	49	20 g reference	Air
Komolafe³²	2000	Stretch sensor	R	HH front	5		40	58		Air, 100°C
Komolafe et al.²⁵	2000	Functional filament	f	HH front	5	7 garments	40	58	DAZ
Liang et al.²⁶	2000	Stretch sensor	c	HH front	3		40			Air
Linz²⁷	2000	Conductive yarn	R	Wascator	20	Total 2 kg CO	40	4M/24	ECE A	Air
Malm et al.²⁸	2012	Conductive paste	R	Wascator	5	+ 1 kg	40	4G/18		Air, air 50°C
Martinez-Estrada et al.²⁹	2012	Moisture sensor	c	HH front	2	+ 1 kg	40		10 g ECE 105
Matsouka et al.³⁰	2012	Textile electrodes	R	Datacolor Ahiba	50		40	30		Air
Ojuroye et al.³¹	2012	Flexible sensors	f	HH front	20	+ 2 kg CO towels	30	15, 37, 42	37 ml, 37 ml softener	Air
Parkova et al.³³		Conductive yarn	R, c	HH front	5		30	31	20 g
Rotzler et al.¹	2000	Conductive tracks	R	Wascator	10	Total 2 kg, CO and PES	20, 40, 60	28, 38, 48	30 g ECE 2	Air
Satharasinghe et al.³⁴	2012	Solar cell	f	HH	25					Air
Schwarz³⁵	2000	Conductive yarn	R	Wascator	25	Total 2 kg, CO	40	4M/25
Tadesse et al.³⁶	2012	Conductive coating	R	HH front	10		(30)	3N
Tadesse et al.³⁷	2012	Conductive coating	R	HH front	10	Protective bag, total 2 kg, PES	30	3N/23	20 ml	Air
Tao et al.³⁸	2012	Conductive yarn, LED, flex PCB	R	Datacolor Ahiba	50		30	30		Air
uz Zaman et al.³⁹		Conductive yarn	R	HH front	10		40	35	20 g
uz Zaman et al.⁴⁰		ECG electrodes	R	HH front	50	Total 2 kg	40	35	20 g Xtra Total
Vervust et al.⁴¹	2000	Stretchable circuit board	R, delamination	HH front	50	Protective bag	40	4N/30	ECE A	Air, dryer

^aBlank spaces indicate non-disclosed information. ^bR: change in resistance; c: change in characteristic; f: change in or loss of function. ^cHH: household washing machine (not further specified), HH front: horizontal axis front-loading household washing machine, HH top: vertical axis top-loading household washing machine. ^dCO: cotton; PES: polyester. ^eThe washing program only refers to ISO 6330 washing programs. The program labels from the 2000 version of the standard were transferred to their 2012 version counterparts to make for easier comparison.

Table 3.

Washing factor ranges for ISO 6330⁴²

Machine type	Number of programs	Time [min]	Temperature [°C]	Mechanical action	Chemistry
A (horizontal axis)	13	7–30	30–92	Soft, gentle, normal	3 powder detergents, 20 g
B (vertical axis)	11	15–21	16–60	Soft, normal	1 liquid, 3 powder detergents, 66 g/100 g
C (vertical axis)	7	14–32	30–40	Soft, normal	1 powder detergent, 1.3 g/l

Table 4.

Wash testing according to other standards^a

Source	Standard	Tested product	Parameter^b	Washing device^c	Cycles	Load	Temperature [°C]	Duration [min]	Detergent	Drying
Frank and Bauch⁴³	DIN EN 20105-C01-5 DIN 54015	Conductive coating	R				40, 50, 60, 95	20, 30, 45 4 h	5 g/l
Jin et al.⁵²	AATCC 135	Conductive tracks		HH top	10–50		40
Lee et al.⁵¹	AATCC M6	Conductive fabric	R	HH top	10	Total 1.8 kg	27	21	66 g reference	Dryer
Li and Tao⁵³	AATCC 135	Conductive yarn	R	HH top	30	Total 1.8 kg, protective bag	40		66 g Castle	Dryer
Liu et al.⁴⁶	AATCC 61	Incontinence monitoring pants	R		20
Sala de Medeiros et al.⁵⁴	AATCC 135	Tribo-electric nanogenerator	R, c	HH top	50	+ 2 kg garments	22	8	Without	Air
Quandt et al.⁴⁴	EN ISO 105-C06	Heartbeat sensor	c	Color tester	10		40	45	4 g/l + bleach	Air
Shahariar et al.⁴⁷	AATCC 61	Conductive ink	R	150 ml water+steel balls	5	Only test samples	49	45	0.24 g
Shahariar et al.⁴⁸	AATCC 61 2a	Conductive paste	R		5
Trindade et al.⁴⁵	ISO 105	ECG sensor	R, c		30		40	45	1 g/l	Air
Xu et al.⁴⁹	AATCC 61 1b	Textile antenna	R, c	150 ml water+ rubber balls	1			20	1 ml + softener	Air
Yokus et al.⁵⁰	AATCC 61 2a	Conductive paste	R	Water + 50 steel balls	20		49		Powder
Zhao et al.⁵⁵	AATCC 135	Tribo-electric nanogenerator	R, c	HH top	20	+ 1.8 kg, protective bag	20	40		Air

A large majority of the sources test conductive textile material (yarn, filaments, or textiles) integrated into a textile base substrate by different methods (knitting, sewing, weaving, embroidering, laminating) or conductive pastes, inks, or coatings applied to textiles. In many cases, these conductive elements are shaped into antennas, electrodes, or conductive tracks. A commonality between those tested products is that they can be considered semi-finished goods, but not fully functional e-textile systems. Some of the examined products have a more complex composition than mere conductive material: Gerhold and Tao et al. test conductive tracks with added LEDs,¹⁷,³⁸ while Ojuroye et al. and Komolafe et al. subject sensors, LEDs, and other modules embedded on kapton-filaments to repeated washing.²⁵,³¹ Satharasinghe et al. test their e-yarn equipped with miniaturized solar cells for washability.³⁴ Only one fully functional system, a fire-fighter suit, is among the tested products.¹⁴

Even though there is no reference given in the standard on how to assess the washability after testing, a similar method is chosen in many of the presented examples from the literature. In 22 of the reviewed sources, a change in resistance after (repeated) washing is used to rate the washability of the tested product. Three of these use more than one method for their assessment.¹²,²³,³³ Washability is also evaluated through changes in the functionality of components or the whole structure,¹⁴,¹⁸,²⁵,³¹,³⁴,⁴¹ as well as altered sensor and antenna properties or characteristics.¹²,²²,²³,²⁶,²⁹,³³ In one instance, the quality of integration is included as a measure for washability: Vervust et al. test their washed samples for delamination.⁴¹ As mentioned above, a large share of the tested e-textiles are not fully functioning systems, but rather single components such as conductive textiles or conductive threads, as well as sensors or antennas without connected modules. For these components, testing for a change in resistance or conductivity is a valid method to assess their washability. In the case of complete, fully functional devices (especially with more complex components present than just conductive textile materials), other parameters have to be used to fully assess the system’s washability. Changes in or (partial) loss of function, changes in sensor or antenna properties, methods already employed by some of the reviewed sources, might provide a better choice.

Another aspect of testing not covered in the standard is the number of wash cycles that should be run to test a product’s washability: only the conditions and procedures are provided. The average number of cycles run in this cluster is 19, but there is a large variation in the number of conducted test cycles (see Table 2): Martinez-Estrada et al. wash their test samples only twice, while Liang et al. test for three cycles.²⁶,²⁹ In contrast, five sources have conducted 50 wash cycles, four of which stem from the University of Lille.¹²,³⁰,³⁸,⁴⁰ Gerhold does not run a predetermined number of cycles, but instead stops testing at the first occurrence of detached components, after 16 cycles.¹⁷ Depending on the type of e-textile and its intended use, the number of wash cycles that a product should be able to withstand without function- or security-compromising damage changes.¹ The difference in number of test cycles could be attributed to this connection. Yet, none of the sources relate the number of cycles to the foreseen use of the tested e-textile. Liang et al. rather claim their stretch sensor provides sufficient washability after testing for only three wash cycles, even though the sensor will be integrated into a dance leotard—a product likely to be washed after each or at least every second use—leading to much higher washing requirements than only three cycles.²⁶

Compliance of the reviewed test methods with the specifications of the standard

Even though all sources in this cluster claim to test according to ISO 6330, the degree of conformity with the testing instructions provided by the standard varies considerably. The evaluation of testing procedures from each cited source reveals pronounced differences in practices, even though the same standard is used as a basis. Hardy et al.,¹⁸ Kazani et al.,^21,22 Linz,²⁷ Schwarz,³⁵ and Tadesse et al.³⁶,³⁷ are among those who follow specifications quite closely. Others rather use the standard as a rough guideline for wash testing.

Washing device: In 18 instances, testing is conducted in a household washing machine, only one of which is a top-loading, vertical axis machine.²³ A programmable, standardized front-loading machine (also called a Wascator)—compliant with ISO 6330 specifications—is employed in six publications.⁶,¹⁶,¹⁷,²⁷,²⁸,³⁵ Of those, four originate at the research institute Fraunhofer IZM. In four of the publications—again stemming from the University of Lille—a Datacolor Ahiba IR, a piece of laboratory dyeing equipment, is used for testing instead of a (standard-compliant) washing machine.¹²,¹⁹,³⁰,³⁸ The level of compliance of the various household machines employed in the cited sources with the requested geometries and other specifications of the standard cannot be estimated from the provided information. But, as research shows, washing in a standard-compliant Wascator resembles a washing process in a regular (front-loading) washing machine in terms of wear on the laundry if a similar or equal washing program is run.¹ The assumption can thus be made that in cases in which a regular household washing machine is employed, the specifications of the standard are met at least to a certain extent, unlike in the cases where the Datacolor device is used.

Load: Few sources give detailed information about the composition and amount of the wash load. Of those that do, five are in accordance with the requirements of the standard: 2 kg total load with additional load consisting of cotton or polyester.¹,¹⁸,²⁷,³⁵,³⁷ Five other sources test with a total load of 1–3 kg,¹⁷,²⁴,²⁸,²⁹,³¹ and one source states that several garments were added to the test samples.²⁵ In four instances, the samples are put in a protective bag,¹³,¹⁷,³⁷,⁴¹ a procedure not within the scope of the standard.

Wash temperature: Less overall variation is found in the choice of washing temperature. Almost two-thirds of the tests are run at a temperature of 40°C, another eight at 30°C, and two each at 20°C^1,²³ and 60°C.¹,¹⁴ The average washing temperature is 39.7°C. From the employed temperatures, 20°C is not within the scope of the standard.

Program and duration: The overall program duration is short. In 19 cases one cycle lasts 30 minutes or less. From the programs listed in the standard, 4M (6A in the 2000 version)—gentle agitation, 40°C, 24 min—is the most widely used.¹,^15–17,²¹,²⁷,³⁵ 3N—normal agitation, 30°C, 30 min³⁶,³⁷—and 4N—normal agitation, 40°C, 30 min¹⁸,⁴¹—are other programs that are found in more than one source.

While some sources claim to wash according to a specific standard program, they use a regular (typically non-programmable) household washing machine. These machines do not normally feature the standard programs within their range of available washing programs. It is unclear if the 6330 programs are indeed installed in the machines used for testing. Another possibility is that these sources rather employ a regular household washing program resembling the stated standard program—like Komolafe et al., who explain that their program is only similar, but not identical to program 6A.²⁵ Ojuroye et al.³¹ and uz Zaman et al.³⁹,⁴⁰ use multiple household washing programs including silk/delicates and wool/handwash, while Rotzler et al.¹ test nine different, self-programmed washing programs to assess washing factor influence in the form of a Design of Experiments (DoE).

Most sources do not elaborate on the reasons for choosing a specific test program. Linz bases their choice of program 6A/4M on research into standard programs most often employed in e-textiles wash testing.²⁷ Ojuroye et al. test their touch and proximity sensor with three household washing programs that represent “typical washing programs for textiles.”³¹ Express and silk, two household programs, were chosen by uz Zaman et al. due to their similar run times.⁴⁰ Kazani et al. wash their conductive textile with 6A/4M due to the program’s relevance to the function of the tested textile, but do not elaborate on what this relevance entails.²² Rotzler et al. model the center point of their DoE washing programs after a household delicates program due to the agreement among many experts that e-textiles should be washed gently.¹,⁶

Detergent: Almost half of the sources do not give information about whether and which kind of detergent is used for testing. From those that do, all but two use powder detergent.³¹,³⁷ Eight sources use a standard-compliant detergent, of which only Kazani et al. and Kivanc et al. indicate the use of the correct dosage.²²,²⁴ Rotzler et al. adjust the amount of detergent due to higher water hardness.¹ Although not included in ISO 6330 detergent specifications, Ojuroye et al. add fabric softener along with detergent.³¹

Drying: Where the employed drying method is provided, the samples are air dried—compliant with standard specifications. Hardy et al. and Vervust et al. also dry some of their samples in a tumble dryer, comparing the effects of the two different drying methods.¹⁸,⁴¹ The results of Hardy et al. show that tumble-drying leads to much more severe damage than washing. Three of the sources do not air-dry the samples in ambient conditions, but use warm (50°C) or hot (100°C) air, a method not given in the standard.²¹,²⁸,³²

Evaluation of the testing methods in this cluster reveals significant disparities even when the same standard is claimed to be used as a basis. Most sources follow the standard only partly—maybe attributed to the available resources and their degree of compliance with standard requirements. Publications from the same institutions show some similarities in wash testing, but there is still variation.

Testing according to other standards

Apart from ISO 6330, other standards that are used as a basis for e-textile wash testing include ISO 105 Textiles—tests for color fastness,^43–45 DIN 54015 Testing of color fastness of textiles—determination of color fastness of dyeings and prints to washing in presence of peroxide,⁴³ AATCC 61 Colorfastness to laundering: accelerated,^46–50 AATCC 6 Colorfastness to acids and alkalis,⁵¹ and AATCC 135 Dimensional changes of fabrics after home laundering,^52–⁵⁵ (Table 4).

Similar to the previous cluster, most of the tested products are conductive textiles or textiles coated with conductive paste or ink. In two cases, the washability of a tribo-electric nanogenerator is assessed.⁵⁴,⁵⁵ Liu et al. test conductive yarn knitted into underpants to monitor incontinence,⁴⁶ Quandt et al. and Trindade et al. test textile sensors,⁴⁴,⁴⁵ and Xu et al. test an antenna.⁴⁹ None of the tested products represents a fully functional system: further components or modules are not included in the testing.

The majority of the sources in this cluster use a change in resistance as an indicator for the washability of the tested products—comparable to the results on testing according to ISO 6330. Of those that provide their method for assessing washability, only Quandt et al. do not use resistance as an indicator; instead, they rely on a change in sensor characteristics.⁴⁴

If testing is done according to the American standards AATCC 135 and AATCC M6, a top-loading washing machine is employed (the predominant type in the USA). Testing according to AATCC 61 is not conducted in a regular washing machine, but in laboratory testing equipment similar to the previously mentioned Datacolor Ahiba IR. Quandt et al. also use a laboratory testing device, the Roaches Washtec color fastness tester.⁴⁴ Unlike all other wash testing reviewed in this research, the method given in AATCC 61 is an accelerated test, with one cycle equivalent to five regular-machine washing cycles, according to the standard. Acceleration is achieved by the addition of steel or rubber balls to the washing container.⁵⁶ The applicability of such harsh treatment for e-textiles has to be assessed, however. Colorfastness, the original scope of the standard, is not inconsiderably affected by friction on the textile surface, so the additional wear generated by the balls can lead to accelerated color loss. For e-textiles that are more susceptible to mechanical damage, this method might not be suitable—especially for products more complex than mere conductive textiles.

The washing temperatures are slightly higher than in the previous cluster, with a mean temperature of 46,2°C. As with the tests according to ISO 6330, 40°C is most prevalent. High washing temperatures of 60°C and more are solely employed by Frank and Bauch⁴³ and only three of the cited sources wash with less than 30°C.⁵¹,⁵⁴,⁵⁵

Air-drying is more common than tumble-drying. In cases where detergent use is elaborated on, powdered detergent is used except for Xu et al., who also add softener along with liquid detergent.⁴⁹

A single wash cycle in this cluster has a duration of between 20 and 45 min. The exemptions are Frank and Bauch, who run cycles of different lengths and temperatures, among them cycles with a duration of 4 h,⁴³ and Sala de Medeiros et al. who wash for 50 cycles of only 8 min each.⁵⁴ The average number of cycles is 22, similar to 19 in the ISO 6330 cluster. If each cycle of the accelerated tests according to AATCC 61 is counted as five cycles, the average cycle count within the cluster of tests according to other standards rises to 40.

Liu et al. give good washability as a requirement for their incontinence monitoring pants as it is projected to be washed frequently during its use.⁴⁶ Due to the results of their testing, several of the sources claim their product features satisfactory,⁵³ unprecedented,⁴⁷ or a good level of⁵⁵ washability, while others only deem the tested e-textiles washable. Li et al. compare the results of the programs normal and delicates, as well as washing with and without a protective bag.⁵³ Quandt et al. assume that the good washability results of their heartbeat sensor originates in the use of conventional textile production techniques (embroidery). Their use of hospital-grade detergent is substantiated by the intended use of their sensor in a medical context.⁴⁴ Similar to the sources from the previous cluster, elaboration on the reasons for choosing specific testing methods and washing parameters is missing in most cases.

Testing under household washing conditions

This cluster contains testing conducted in household washing machines (top-loading vertical axis and front-loading horizontal axis) without a standard as a guideline. Testing parameters for each of the sources can be found in Table 5.^57–75

Table 5.

Wash testing under household conditions^a

Source	Tested product	Parameter^b	Washing device^c	Cycles	Load	Temperature [°C]	Duration [min]	Detergent	Drying
Ankhili et al.⁵⁷	ECG electrodes	R, c	HH front	50	Total 2 kg	40	35	30 ml Xtra total	Air
Berglund et al.⁵⁸	Stretch sensors	R, delamination	HH top	5				Arm & Hammer	Air, dryer
Björninen et al.⁵⁹	RFID tag	c	HH	10		40
Gaubert et al.⁶⁰	Conductive yarn	R, c, color	HH front	30	+1.8 kg garments	30	60	70 g powder, 60 ml liquid, without, 7 g Na percarbonate	Air
Gui et al.⁶¹	LED module	f	HH top	2		25	15	With and without	Air
Ismar et al.⁶³	Conductive yarn	R	HH	1		30			Air
Janczak et al.⁶⁴	Electroluminescent element	f	HH	10		40	30		Air
Kellomäki et al.⁶⁵	Textile antenna	c	HH	10	Extra load, protective bag	60	2.5 h	Liquid	Air
Lam et al.⁶⁶	Conductive ink	R	HH top	10				With
Molla et al.⁶⁷	Conductive yarn and LEDs	R	HH top	10		30	60	2.4 oz ALL free and clear	Dryer
Ryan et al.⁶⁸	Conductive yarn	R	HH	4	+2 towels, protective bag	30	50	20 ml color	Air
Tang et al.⁶⁹	Conductive textiles	R	HH top	6	+1 kg garments		35		Air
Tao et al.⁷⁰	Activity monitor	f	HH	30			30		Air, 40°C
uz Zaman et al.⁶²	Conductive yarn	R	HH front	5			23, 36	1.25 g/l	Air
uz Zaman et al.⁷¹	Conductive yarn	R		10					Air
Wang et al.⁷²	RFID tag	c	HH	15		40		With
Zeagler et al.⁷³	Conductive tracks	R	HH top	6		Warm		1 oz ALL ultra	Air
Zhou et al.⁷⁴	Textile antenna	R	HH front	8	Protective bag	30	20, 60		Air
Zysset et al.⁷⁵	Functional filaments	f, c	HH front	5		30	47	Woolite mild

Table 6.

Wash testing with alternative methods.^a

Source	Tested product	Parameter^b	Method	Cycles	Temperature [°C]	Duration	Detergent
Cai et al.⁷⁷	Heating textile	c	Stirring in 100 ml water	10		12 h	Without
Carey et al.⁷⁸	Conductive paste	c	100 ml water, no agitation	20	50	30 min	0.2 g NaCarb 0.5 g detergent
Du et al.⁸⁵	Conductive textile	R	Continuous mechanical washing	1		40 h
Gaubert et al.⁶⁰	Conductive textile	R, c, color	500 ml water, no agitation	1	30	30 h	3.5 g powder, 3 ml liquid, without, 0.35 g NaCarb.
Gorgutsa et al.⁸²	Conductive filaments	c	Stirring in 1 L water	20	40/60	15 min
Guo et al.⁷⁹	Conductive textile	R	Water, no agitation	1		1500 min
Jinno et al.⁸³	Solar cells	c	No agitation/ stirring in water			30 min	With
Lin et al.⁸⁶	Sleep monitor	R	Handwashing in water	1	20	20 min	Without
Ren et al.⁸⁴	Conductive textile	R	Oscillating dying machine	10	60	30 min	0.2 g NaCarb, 0.5 g detergent
Scheulen et al.⁸⁰	Contacting	Corrosion	Water, no agitation	1		1 week	Standard detergent
Tang et al.⁶⁹	Conductive textile	R	Stirring in water	6		48 h
Virkki et al.⁸¹	RFID tag	c	Water, no agitation	10	60/40	60 min/40 min	Without/0.2 dm³

^ablank spaces indicate non-disclosed information. ^bR: change in resistance, c: characteristic.

The tested e-textiles are mainly conductive textiles or sensors, electrodes, antennas, and RFID tags made from conductive textile material without further components. Janczak et al. test printed electroluminescent displays.⁶⁴ Gui et al. and Molla et al. include LEDs,⁶¹,⁶⁷ Zysset et al. use sensor modules on functional polymer filaments,⁷⁵ and Tao et al. use electronic components embedded in Polydimethylsiloxane (PDMS).⁷⁰ Consistent with the standard-based testing practices, change in resistance is the predominant parameter to assess washability. Besides an increase in resistance, Berglund et al. include the extent of delamination as a measure for washability, while Gaubert et al. also consider a change in color of the tested metallized textiles.⁵⁸,⁶⁰ Changes in functionality or sensor and antenna characteristics are also employed to rate and assess washability.

In almost half the cases where a washing temperature is given, testing is done at 30°C; 40°C has the second highest incidence. Gui et al. wash at 25°C and Kellomäki et al. at 60°C.⁶¹,⁶⁵ Only four sources wash for more than 10 cycles.⁵⁷,⁶⁰,⁷⁰,⁷² Both the washing temperatures and the average number of washing cycles are lower, but the average duration of a single cycle is significantly longer (47 min) than in the two previous clusters.

The use of liquid detergent is more common than in standard-based testing.⁵⁷,⁶⁰,⁶⁵,⁶⁷,⁶⁸,⁷³,⁷⁵ As not all sources provide information about detergent use, this number might be even higher. Air-drying is predominant; a tumble dryer is used only on two occasions. Similar to the results of Hardy et al., the research of Berglund et al. reveals tumble-drying to be more damaging to their stretch sensors than washing.⁵⁸

In some cases, test samples are not only washed in a washing machine, but also placed in water (with and without detergent) for an extended amount of time in a parallel test. This is done either to compare results from washing with those from immersion only, or to evaluate the influence of moisture and water on the tested samples separately from washing.⁶¹,⁶⁵,⁶⁸ Additional testing for Gaubert et al. and Tang et al. is so extensive that both sources are also included in the following cluster, testing with alternative methods.

Compared to the previous two clusters, a larger number of sources give reasons for choosing specific washing conditions or test protocols. Ankhili et al., Gaubert et al., Lam et al. and Molla et al. choose a household washing program and machine because they claim that a user will wash their e-textile in a similar manner when using the product.⁵⁷,⁶⁰,⁶⁶,⁶⁷ Uz Zaman et al. use commercial instead of standardized detergent because of similar reasoning.⁷¹ Gaubert et al. additionally justify their choice of program by referring to their garment manufacturer client’s specifications, while Zeagler et al. argue that warm washing with regular agitation provides harsher conditions, so if the tested samples withstand this treatment, they would withstand gentler washing as well.⁶⁰,⁷³ Björninen et al. compare their washing results to those of other publications in which similar e-textiles have been washed for the same amount of washing cycles, implicating a choice of testing parameters based on literary research and the need for comparability.⁵⁹

With lower temperatures, longer cycles, and a higher incidence of liquid detergent, testing in this cluster resembles actual (gentle) household washing more closely than the standard-based testing. A washing temperature of 30°C (or lower) is generally recommended for delicate textiles, and is the default setting for many washing programs aimed at delicate items.⁷⁶ A program such as silk/delicates, for a front-loading machine, has a duration of around 45 min and a default temperature of 30°C—close to the average cycle duration of 47 min and average temperature of 35°C in this cluster.⁶

Testing with alternative methods

In some of the sources, wash testing is not conducted in a washing machine, but with alternative methods (Table 6). These methods include placing the samples in water or wash liquor (without further agitation)⁶⁰,^77–81 and stirring the samples in a beaker.⁶⁹,⁷⁷,⁸²,⁸³ Others employ laboratory testing equipment, such as the previously mentioned dyeing unit Datacolor Ahiba,⁸⁴ or subject the samples to “continuous mechanical washing.”⁸⁵ Lin et al. wash their samples by hand in water without detergent present.⁸⁶ Gaubert et al.⁶⁰ and Tang et al.⁶⁹ also test their samples under household conditions, comparing results. Carey et al. claim their test method represents the industry standard and reference Ren et al., who indeed use a similar method—although they test for only 10 cycles instead of 20 and at a different temperature.⁷⁸,⁸⁴ Gorgutsa et al. reason that their method represents common practice and refer to previous studies as well as the manufacturer’s guidelines.⁸²

The complexity of the tested e-textiles is quite low. As in the three previous clusters, a majority are conductive textiles with no further modules. The solar cells tested by Jinno et al. are among the most complex products in the alternative washing methods cluster. Although Guo et al. test graphene paper, they claim that it constitutes an e-textile.⁷⁹ Due to the test set-up of the alternative methods, the test samples in this cluster are washed without any additional load.

In half of the cases, a change in resistance is the indicator for washability—the lowest percentage of all the clusters. Shifts in characteristic properties are utilized just as often. Scheulen et al. only test for occurrence of corrosion in their magnetic contacts.⁸⁰

In contrast to the previously mentioned testing procedures, some of the alternative tests run for a considerably longer time, from 12 h up to 1 week.⁶⁰,⁶⁹,⁷⁷,⁷⁹,⁸⁰,⁸⁵ The average number of test cycles is lower than for the other clusters, which relates to the number of very long-running tests in which fewer cycles are conducted. Testing temperatures are highest when alternative methods are employed, with an average testing temperature of 47°C; in one-third of the cases the washing temperature is at or above 50°C.⁷⁸,⁸¹,⁸²,⁸⁴

The comparability of the alternative methods with actual wash cycles is not sufficiently researched. Only Tang et al.⁶⁹ test their samples both by stirring in water and in a household washing machine, while Gaubert et al. compare the household washing results for their conductive textiles with placing them in water with different types and amounts of detergent.⁶⁰ Gaubert et al. find in their research that if the tested conductive textiles are only exposed to a single one of the four Sinner’s factors—in their case either chemistry in the form of detergents or mechanical agitation—the resulting damage is quite limited. Not until multiple factors act and interact at the same time do significant losses in conductivity occur.⁶⁰,⁶⁹ The methods employed in this cluster are thus (possibly) unreliable for a correct estimation of washability under real usage conditions. This is especially true where samples are just put into water without agitation, and in one case even without detergent.⁸¹ Nevertheless, washability of the tested product is deemed satisfactory in most sources. Cai et al. claim their heating textile is just as washable as regular textiles.⁷⁷ To assess the influence of a single factor of the washing process (e.g., water, detergent, or washing temperature), the alternative methods might be able to provide valid results, though.

Critical evaluation of current e-textile wash testing practices

This research on test methods to assess washability of e-textiles reveals a large range of varying practices. Within the following section, the suitability of the employed methods is considered.

Comparison of average values for all clusters: Table 7 gives an overview of the average values of cycle count, temperature, cycle duration, total washing time, and the incidence of a change in resistance as a measure for washability for all four clusters. If very long cycles are omitted, the average duration is very similar for standard-based testing and alternative methods testing at 33, 32, and 32 min, with household tests taking significantly longer on average at 47 min. The number of conducted cycles is higher in standard-based testing. Even though the cycles are longer, the total average washing time with household methods is lower than in standard-based testing due to the lower cycle number. At 45.0°C, 47.1°C, and 46.2°C, the temperatures in the clusters of alternative methods and other standards are higher than in the other two clusters.

Table 7.

Average values for all clusters

Cluster	Cycles	Temperature [°C]	Duration [min]	Total washing time [h]^a	ΔR as parameter [%]
ISO 6330	19	39.7	33	10.5	69
Other standards	22	46.2	32	11.7	77
Other standards^b	40	46.2	32	21.5	77
Household	12	35.4	47	9.0	63
Alternative methods	8	45.0	1634	217.8	50
Alternative methods^c	12	47.1	32	6.5	50

^atotal washing time = number of cycles · duration. ^bIf one accelerated test cycle is counted as five regular wash cycles. ^cIf very long cycles are excluded.

Are the employed testing methods able to adequately estimate the washability of the tested products? Can equivalent, accelerated, or alternative tests obtain correct results for reliability estimations? A change in resistance is the parameter most often used to assess washability, but is not necessarily useful for fully functional systems. Since a majority of the e-textiles tested in the researched publications are only conductive textiles or otherwise non-complex in composition, a change in resistance is an adequate measure, however.

Some of the reviewed papers suggest that alternative test methods (including the standard-based tests not conducted in washing machines) might not be able to provide correct estimates of washability under real washing conditions. Accelerated testing according to AATCC 61 might be equally unreliable—a lack of comparative testing does not allow for a conclusive verdict. The standard (which requires its execution in laboratory testing equipment), although conceived for textile washing tests, is not intended to assess general washability, only colorfastness. The influencing factors that affect colorfastness are not equal to those that affect washability. The standard’s potential for an accurate estimation of washability—especially for e-textiles—is therefore disputable. On the other hand, if the accelerated tests according to AATCC 61 are factored into the average cycle count of the testing according to other standards cluster with five cycles for each accelerated cycle (as intended by the standard), the average number of wash cycles for this cluster increases to 40 (from 22). This is a much higher cycle count compared to the other three clusters. The use of accelerated testing can thus lead to an increased number of overall wash cycles, enabling possibly a more accurate assessment of washability—especially for e-textiles with a high projected cleaning frequency. Due to resource and time constraints, conducting an equivalent number of non-accelerated tests for new e-textile developments might not be feasible. The testing methods have to be specifically conceived for e-textiles, though, to ensure that the acceleration does not lead to failure mechanisms that would not occur in non-accelerated testing.⁸⁷ Wash testing results from Rotzler et al. show that cracks in textile metallization only occur above a threshold washing temperature.¹ An accelerated test featuring a higher washing temperature could thus lead to a worse estimate of washability compared to repeated washing at the lower temperature. The same might be true for an increased mechanical strain through the addition of steel balls to the washing container, the method provided by AATCC 61. The development of suitable accelerated or equivalent testing protocols needs to be preceded by a thorough analysis of failure mechanisms and the matching contributing influence factors for a range of different e-textiles.⁸⁷

Are the test protocols capable of cleaning the product? The main purpose of a washing process is the ensuing cleanliness of the laundry. This aspect is not addressed by any of the reviewed sources except Rotzler et al.¹ Neither is the cleaning capability taken into consideration when choosing a suitable testing protocol. The intended use and the resulting typical product life cycle should be factored in before choosing reliability-testing methods. With regard to wash testing, the kind of staining a product will experience as well as its projected cleaning frequency (e.g. underwear/sports clothing: after every use; jackets/outerwear: only a few times during the life cycle) have to be taken into account. Protocols employed in the washability evaluation of a product should be capable of removing use-specific staining reliably and satisfactorily. The product in turn should withstand these wash protocols for as many cycles as are to be expected during its intended life span. Only then can the product be deemed washable.¹ Within the scope of an e-textile washing or reliability standard, the cleaning capabilities of the provided washing programs could be included, facilitating the choice of a suitable testing method for e-textile developers. The methods of the aforementioned IEC 60456 could be used as a basis for the assessment of cleaning capabilities for future e-textile washing programs.⁸⁹

Does the test protocol include safety concerns? Because of the presence of electronic components, or at least electrically conductive materials in e-textiles, possible health or safety issues could arise for the user (or the environment) in the case of a damaged or malfunctioning product caused by the washing process. Potential dangers include electric shock, overheating, and ignition. Toxic or otherwise problematic substances can contaminate the washing water—metallized textiles are prone to losing their metal coating over time during washing.⁸⁸ So far, these security concerns are not properly addressed by any of the reviewed publications. The focus rather lies on retaining functionality.

How do the chosen wash programs relate to actual customer laundry practices and industry suggestions? The average temperature for the household cluster is 35°C. Combined with the average cycle duration of 47 min and a high incidence of liquid detergent, the values of this cluster are a good representation of gentle household washing conditions. On the other hand, the standard-based testing with a higher cycle count reflects the number of washing cycles during the life cycle of most actual textile products to a greater extent. The average washing temperatures in standard-based testing and the alternative methods cluster are much higher than the 30°C that are recommended (for textiles in general and especially so for delicate laundry items) by a growing number of detergent industry and sustainability experts. With campaigns like I PREFER 30, these efforts are communicated to consumers, encouraging a more energy-conscious and laundry-preserving washing behavior.⁹⁰ The default temperature for a majority of washing programs aimed at delicate laundry items in household washing machines is already set to 30°C.⁷⁶ Furthermore, some types of e-textiles are damaged by higher washing temperatures due to the effects from a mismatch of the coefficient of thermal expansion (CTE) of the involved materials¹—another argument for testing at rather lower temperatures than current practice.

Do the currently used test programs allow for some kind of comparability? A large share of the cited sources test similar materials: conductive textiles or yarns. The methods employed differ profoundly, however, making washability comparisons difficult. This large variation is the result of a lack of e-textile-specific standardization, as researchers are unable to draw their methodology from a common source. Yet even when testing is done at the same institution, the employed methods are often not consistent (enough) for a comparable appraisal of washability. Until standards are implemented, testing at the same—or even at several connected—institutions should be as uniform as possible to achieve at least local comparability.

Taking diverse product requirements into account, a range of testing protocols should exist for e-textiles—not unlike the different washing programs provided by ISO 6330—but the overall variety should be smaller than in the current situation. An e-textile specific wash testing standard will be able to alleviate this lack of comparability.

Do the specific test protocols reflect the intended use case of the products and the product type? The majority of sources researched in this paper do not base their choice of washing protocol on the type of tested product or its intended use. Apart from a few exceptions, no selection criteria are given and the employed methods are either (seemingly) arbitrary or based on common practice. Since the cleaning needs and ensuing reliability requirements of an e-textile during its lifetime strongly depend on the product type and its usage conditions, both should be considered when choosing a suitable protocol to assess washability.

If a standard is used, how strictly are the guidelines followed? As the analysis shows, most sources that use ISO 6330 as a basis for their testing follow the standard quite loosely, and even in cases with greater accordance not all guidelines are followed. This lack of compliance could be attributed to the standard being conceived for textile (not e-textile) testing and thus not completely meeting e-textile-specific requirements for wash testing. Another reason could be a lack of standard-compliant equipment and resources (like a climatized lab or water of a specific hardness). Where other standards are used, the extent of compliance is generally higher than with testing according to ISO 6330, but there are still differences in practices.

Is there insight into the influence of different factors of the washing process on e-textiles? Very few sources research general e-textile washability. Gaubert et al. investigate the influence of different kinds of detergent on the washing results of conductive textiles.⁶⁰ Rotzler et al. research the influence of washing temperature, cycle duration, and mechanical strain on multiple types of textile-integrated conductive tracks, as well as the influence of different textile substrates on the washability.¹ The effect of textile substrates is also examined by Kazani et al.²¹ Toward the development of suitable (standardized) test methods for e-textiles or prospective e-textile-specific washing programs for household washing machines, more research into how different e-textiles are influenced by which kind of washing conditions will be necessary.

Conclusion

The presented insight into current e-textile wash testing methods is limited by the researched sources’ lack of fully disclosed methodology on wash testing. Unavailable information on industry practices further narrows the degree of overall understanding of the topic. Despite these limitations, this paper is able to underscore the need for e-textile-specific standardization to overcome the existing lack of comparability between differing employed methods. Even though no proper e-textile standards exist yet, in 60% of the reviewed publications a standard is already used as the basis for their washability testing—with varying degrees of compliance. This number shows that the willingness to use standards is high among researchers.

The currently used standards all stem from the textile field, lacking an adequate consideration of the integrated electrically conductive and electronic components of e-textiles and potential safety concerns that might arise. A future standard should provide a range of washing programs for different kinds of washing devices. These programs should reflect different conceivable use cases for e-textiles concerning cleaning frequency, hygiene requirements, and possible staining. Different requirements stemming from the respective materials and manufacturing methods employed for a specific e-textile need to be considered as well. To allow for a feasible way to estimate long-term washing reliability, accelerated or equivalent test methods will have to be provided as well. The scope of such a standard should include suitable evaluation methods, enabling users of the standard to reliably and comparably assess their product’s washability. To develop such specialized testing methods, more insight into how different washing conditions affect various types of e-textiles is needed—especially if accelerated testing methods are to be developed. Only a joint effort of interdisciplinary experts from all areas involved in e-textile development will lead to suitable standardization.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Sigrid Rotzler

References

Rotzler

Kallmayer

Dils

, et al. Improving the washability of smart textiles: influence of different washing conditions on textile integrated conductor tracks. J Text Inst 2020; 111(12): 1766–1777.

Reumann

R-D.

Mechanisches Formänderungsverhalten textiler Materialien. In: Reumann R-D (ed) Prüfverfahren in der Textil- und Bekleidungstechnik. Berlin: Springer, 2000, pp.57–125.

Bisenius

Product safety of the internet of things. IEEE Consumer Electronics Magazine 2017 6(3): 137–139.

Wagner

Waschmittel. 5th ed. Weinheim: Wiley VCH, 2017.

Ohnemus

J and

Rasel

FashionTech: Smart Textiles. Mannheim: Zentrum für Europäische Wirtschaftsforschung GmbH, 2018.

Rotzler

Einfluss der Sinnerschen Faktoren sowie der textilen Substrate auf die Waschbarkeit textilintegrierter Leiterbahnen. Master’s Thesis. Hochschule für Technik und Wirtschaft HTW Berlin, Germany, 2018.

Moazzem

Daver

Crossin

, et al. Assessing environmental impact of textile supply chain using life cycle assessment methodology. J Text Inst 2018; 109: 1547–1585.

Wilson

Laing

Fabrics and garments as sensors: a research update. Sensors 2019; 19: 3570.

Alzaidi

Zhang

Bajwa

, et al. Smart textiles based wireless ECG system. In: 2012 IEEE Long Island systems, applications and technology conference (LISAT), 4 May 2012, pp.1–5. Farmingdale, NY: IEEE.

10.

Shyamkumar

Rai

, et al. Wearable wireless cardiovascular monitoring using textile-based nanosensor and nanomaterial systems. Electronics 2014; 3: 504–520.

11.

ISO

6330:2012. Textiles—domestic washing and drying procedures for textile testing.

12.

Ankhili

Tao

Cochrane

, et al. Washable and reliable textile electrodes embedded into underwear fabric for electrocardiography (ECG) monitoring. Materials 2018; 11(2): 256.

13.

Baribina

Baltina

Oks

, et al. Application of additional coating for conductive yarns protection against washing. Key Eng Mater 2018; 762: 396–401.

14.

Blecha

Soukup

Kaspar

, et al. Smart firefighter protective suit: functional blocks and technologies. In: 2018 IEEE international conference on semiconductor electronics. Kuala Lumpur, Malaysia, 15-17 August 2018. Piscataway, NJ: IEEE.

15.

Erdem

Yesilpınar

, and Senol

Design of a TENS knee pad with integrated textile electrodes. In: 7th international technical textiles congress, Izmir, Turkey, 14-17 April 2018, pp.237–245.

16.

Foerster

Untersuchungen zu Eigenschaften von Nanosilberschichten auf Polyamidfasern. Studienarbeit. Technische Universität Berlin, Germany, 2010.

17.

Gerhold

Researches on ultrasonic-welded electrical interconnections at smart textiles using nonconductive adhesives. Master’s Thesis. Hochschule für Technik und Wirtschaft HTW Berlin, Germany, 2018.

18.

Hardy

Rahemtulla

Satharasinghe

, et al. Wash testing of electronic yarn. Materials 2020; 13(5): 1228.

19.

Huang

T-H

Tao

Y-C

, et al. A novel design of e-textile integration for physiological monitoring and lighting. J Fashion Tech Text Eng 2018; S4: 10.

20.

Kayacan

Bulgun

, et al. Design methodology and performance studies of a flexible electrotextile surface. Autex Res J 2015; 15(3): 153–157.

21.

Kazani

Hertleer

Mey

, et al. Electrical conductive textiles obtained by screen printing. Fibres Text East Eur 2012; 90: 57–63.3.

22.

Kazani

Declerq

Scarpello

, et al. Performance study of screen-printed textile antennas after repeated washing. Autex Res J 2014; 14(2): 47–54.

23.

Kim

Lee

Evaluation of laundering durability of electro-conductive textile dip-coated on para aramid knit with graphene/waterborne polyurethane composite. Fibers Polym 2018; 19(11): 2351–2358.

24.

Kivanc

Bahadir

SK.

Effects of home laundering on electrical resistance of signal transmission lines on colored e-textiles. J Energy Power Eng 2017; 11: 336–344.

25.

Komolafe

Torah

Wei

, et al. Integrating flexible filament circuits for e-textile applications. Adv Mater Technol 2019; 4: 1900176.

26.

Liang

Stewart

, and Bryan-Kinns

Design of textile knitted stretch sensors for dance movement sensing. Proceedings 2019; 32: 14.

27.

Linz

Analysis of failure mechanisms of machine embroidered electrical contacts and solutions for improved reliability. PhD Thesis. Universiteit Gent, Belgium, 2012.

28.

Malm

Seoane

, and Nierstrasz

Characterisation of electrical and stiffness properties of conductive textile coatings with metal flake-shaped fillers. Materials 2019; 12: 3537.

29.

Martinez-Estrada

Moradi

Fernández-Garcia

, et al. Impact of manufacturing variability and washing on embroidery textile sensors. Sensors 2018; 18(11): 3824.

30.

Ojuroye

Torah

, and Beeby

Modified PDMS packaging of sensory e-textile circuit microsystems for improved robustness with washing.

Microsyst Technol 2019. DOI: 10.1007/s00542-019-04455-7

31.

Komolafe

Reliability and interconnections for printed circuits on fabric. PhD Thesis. University of Southampton, UK, 2016.

32.

Parkova

Vilumsone

Insulation of flexible light emitting display for smart clothing. WIT Trans Built Environ 2014; 137: 603–614.

33.

Satharasinghe A, Hughes-Riley T, and Dias T. Wearable and washable photovoltaic fabrics. In: 36th European photovoltaic solar energy conference and exhibition, Marseille, 9-13 September 2019, pp.42–45.

34.

Schwarz

Electro-conductive yarns: their development, characterization and applications. PhD Thesis. Universiteit Gent, Belgium, 2011.

35.

Tadesse

Loghin

Chen

, et al. Effect of liquid immersion of PEDOT: PSS-coated polyester fabric on surface resistance and wettability. Smart Mater Struct 2017; 26: 065016.

36.

Tadesse

Mengistie

Chen

, et al. Electrically conductive highly elastic polyamide/lycra fabric treated with PEDOT:PSS and polyurethane. J Mater Sci 2019; 54: 9591–9602.

37.

Tao

Koncar

Huang

T-H

, et al. How to make reliable, washable, and wearable textronic devices. Sensors 2017; 17: 673.

38.

uz Zaman

Tao

Cochrane

, et al. Launderability of conductive polymer yarns used for connections of e-textile modules: mechanical stresses. Fibers Polym 2019; 20(11): 2355–2366.

39.

uz Zaman

Tao

Cochrane

, et al. Understanding the washing damage to textile ECG dry skin electrodes, embroidered and fabric-based; set up of equivalent laboratory tests. Sensors 2020; 20(5): 1272.

40.

Vervust

Buyle

Bossuyt

, et al. Integration of stretchable and washable electronic modules for smart textile applications. J Text Inst 2012; 103(10): 1127–1138.

41.

DIN EN ISO 6330:2012. Textilien – Nichtgewerbliche Wasch- und Trocknungsverfahren zur Prüfung von Textilien.

42.

Frank

Bauch

Hochfunktionale leitfähige Beschichtungen aus CNT/Polypyrrol-Kompositbeschichtungen für intelligente Textilien. Research Report, Deutschen Institute für Textil- und Faserforschung, Germany, 2013.

43.

Quandt

Braun

Ferrario

, et al. Body-monitoring with photonic textiles: a reflective heartbeat sensor based on polymer optical fibres. Interface 2017; 14: 20170060.

44.

Trindade

Martins

Miguel

, et al. Design and integration of wearable devices in textiles. Sens Transducers 2014; 183(12): 42–47.

45.

Liu

Wang

, and Lao

TT.

A novel solution of monitoring incontinence status by conductive yarn and advanced seamless knitting techniques. J Eng Fibers Fabr 2012; 7(4): 50–56.

46.

Shahariar

Kim

Soewardiman

, et al. Inkjet printing of reactive silver ink on textiles. ACS Appl Mater Interfaces 2019; 11(6): 6208–6216.

47.

Shahariar

Kim

Bhakta

, et al. Direct-write printing process of conductive paste on fiber bulks for wearable textile heaters. Smart Mater Struct 2020. Epub ahead of print July 3. DOI: 10.1088/1361-665X/ab8c25.

48.

Eike

Cliett

, et al. Durability testing of electronic textile surface resistivity and textile antenna performance. Text Res J 2019; 89(18): 3708–3721.

49.

Yokus

Foote

, and Jur

JS.

Printed stretchable interconnects for smart garments: design, fabrication, and characterization. IEEE Sens J 2016; 16(22): 7967–7976.

50.

Lee

Chen

C-C

, et al. Laundering reliability of electrically conductive fabrics for e-textile applications. In: 2019 IEEE 69th electronic components and technology conference (ECTC), Las Vegas, NV, 28-31 May 2019, pp.1826–1832. Piscataway, NJ: IEEE.

51.

Jin

Matsuhisa

Lee

, et al. Enhancing the performance of stretchable conductors for e-textiles by controlled ink permeation. Adv Mater 2017; 29(21): 1605848.

52.

Tao

XM.

Three-dimensionally deformable, highly stretchable, permeable, durable and washable fabric circuit boards. Proc R Soc A 2014; 470: 20140472.

53.

Sala de Medeiros

Chanci

Moreno

, et al. Waterproof, breathable, and antibacterial self-powered e-textiles based on omniphobic triboelectric nanogenerators. Adv Funct Mater 2019; 29: 1904350.

54.

Zhao

Yan

Liu

, et al. Machine-washable textile triboelectric nanogenerators for effective human respiratory monitoring through loom weaving of metallic yarns. Adv Mater 2016; 28: 19267–10274.

55.

AATCC61a. Test method for colorfastness to laundering: accelerated.

56.

Ankhili

uz Zaman

Tao

, et al. Washable embroidered textile electrodes for long-term electrocardiography monitoring. Text Leather Rev 2019; 2(3): 126–135.

57.

Berglund

Coughlin

Gioberto

, et al. Washability of e-textile stretch sensors and sensor insulation. In: ISWC ’14: Proceedings of the 2014 ACM international symposium on wearable computers, Seattle, Washington, USA, 13-17 September 2014, pp.127–128. New York: Association for Computing Machinery.

58.

Björninen

Virkki

Sydänheimo

, et al. Impact of recurrent washing on the performance of electro-textile UHF RFID tags. In: 2014 IEEE RFID technology and applications conference (RFID-TA), Tampere, Finland, 8-9 September 2014, pp.251–255. Piscataway, NJ: IEEE.

59.

Gaubert

Gidik

Bodart

, et al. Investigating the impact of washing cycles on silver-plated textile electrodes: a complete study. Sensors 2020; 20(6): 1739.

60.

Gui

Tan

Wang

, et al. Spraying printing of liquid metal electronics on various clothes to compose wearable functional device. Sci China Technol Sci 2017; 60(2): 306–316.

61.

uz Zaman

Tao

Cochrane

, et al. IPC white paper on reliability and washability of smart textile structure: readiness for the market. White Paper IPC-WP-024. IPC, 2018.

62.

Ismar

uz Zaman

Bahadir

, et al. Seam strength and washability of silver coated polyamide yarns. In: 18th world textile conference (AUTEX 2018), Istanbul, Turkey, 20-22 June 2018, p. 012053. Bristol: IOP Publishing.

63.

Janczak

Zych

Raczynski

, et al. Stretchable and washable electroluminescent display screen-printed on textile. Nanomaterials 2019; 9: 1276.

64.

Kellomäki

Virkki

Merilampi

, et al. Towards washable wearable antennas: a comparison of coating materials for screen-printed textile-based UHF RFID tags. Int J Antennas Propag 2012; 2012: 476570.

65.

Lam

Jo K

Kim C-H

, et al. Calligraphic ink enabling washable conductive textile electrodes for supercapacitors. J Mater Chem A 2016; 4: 4082–4088.

66.

Molla

MTI

Compton

, and Dunne

LE.

Launderability of surface-insulated cut and sew e-textiles. In: ISWC ’18: Proceedings of the 2018 ACM international symposium on wearable computers, Singapore, 8-12 October 2018, pp.104–111. New York, NY: Association for Computing Machinery.

67.

Ryan

Mengistie

Gabrielsson

, et al. Machine-washable PEDOT:PSS dyed silk yarns for electronic textiles. ACS Appl Mater Interfaces 2017; 9(10): 9045–9050.

68.

Tang

Yao

, et al. Highly machine-washable e-textiles with high strain sensitivity and high thermal conduction. J Mater Chem C 2020; 8: 2741–2748.

69.

Tao

Huang

T-H

Shen

C-L

, et al. Bluetooth low energy based washable wearable activity motion and electrocardiogram textronic monitoring and communicating system. Adv Mater Technol 2018; 3: 1700309.

70.

uz Zaman

Tao

Cochrane

, et al. Market readiness of smart textile structures: reliability and washability. In: Aegean international textile and advanced engineering conference (AITAE2018), Mytilene, Greece, 5-7 September 2018, p. 012071. Bristol: IOP Publishing.

71.

Wang

Chong

Virkki

, et al. Towards washable electrotextile UHF RFID tags: reliability study of epoxy-coated copper fabric antennas. Int J Antennas Propag 2015; 2015: 424150.

72.

Zeagler

Audy

Gilliland

, et al. Can I wash it? The effect of washing conductive materials used in making textile based wearable electronic interfaces. Technical Report. Georgia Institute of Technology, USA, 2013.

73.

Zhou

Padgett

Cai

, et al. Single-layered ultra-soft washable smart textiles for all-around ballistocardiograph, respiration, and posture monitoring during sleep. Biosens Bioelectron 2020; 155: 112064.

74.

Zysset

Cherenack

Kinkeldei

, et al. Weaving integrated circuits into textiles. In: International symposium on wearable computers (ISWC) 2010, Seoul, 10-13 October 2010, pp.1–8. Piscataway, NJ: IEEE.

75.

Rotzler

Evaluierung bestehender Prüfmethoden zur Wäscheschonung & deren Anwendbarkeit auf Sonderprogramme. Bachelor Thesis. Hochschule für Technik und Wirtschaft HTW Berlin, Germany, 2017.

76.

Cai

Song

, et al. Warming up human body by nanoporous metallized polyethylene textile. Nat Commun 2017; 8: 496.

77.

Carey

Cacovich

Divitini

, et al. Fully inkjet-printed two-dimensional material field-effect heterojunctions for wearable and textile electronics. Nat Commun 2017; 13(44); 8: 12012.

78.

Guo

Dun

, et al. Ultrathin, washable, and large-area graphene papers for personal thermal management. Small 2017; 13(44): 1702645.

79.

Scheulen

Schwarz

, and Jockenhövel

Reversible contacting of smart textiles with adhesive bonded magnets. In: ISWC ’13: Proceedings of the 17th annual international symposium on wearable computers, Zürich, Switzerland, 9-12 September 2013, pp.131–132.

80.

Virkki

Björninen

Kellomäki

, et al. Reliability of washable wearable screen printed UHF RFID tags. Microelectron Reliab 2014; 54: 840–846.

81.

S Gorgutsa, K Bachus, S LaRochelle, et al. Washable hydrophobic smart textiles and multi-material fibers for wireless communication. Smart Mater Struct 2016; 25: 115027.

82.

Jinno

Fukuda

, et al. Stretchable and waterproof elastomer-coated organic photovoltaics for washable electronic textile applications. Nat Energy 2017; 2: 780–785.

83.

Ren

Wang

Zhang

, et al. Environmentally-friendly conductive cotton fabric as flexible strain sensor based on hot press reduced graphene oxide. Carbon 2017; 111: 622–630.

84.

Tang

, and Ouyang

Highly washable e-textile prepared by ultrasonic nanosoldering of carbon nanotubes onto polymer fibers. J Mater Chem C 2018; 6: 883–889.

85.

Lin

Yang

, et al. Large-scale and washable smart textiles based on triboelectric nanogenerator arrays for self-powered sleeping monitoring. Adv Funct Mater 2017; 28: 1704112.

86.

Birolini

Reliability engineering: theory and practice. 5th ed. Berlin: Springer Verlag, 2007.

87.

Gaubert

Gidik

Bodart

, et al. Quantification of the silver content of a silverplated nylonelectrode according to the nature of the laundering detergent. In: 7th international conference on intelligent textiles & mass customisation (ITMC 2019), Marrakech, Morocco, 13-14 November 2019. Bristol: IOP Publishing.

88.

IEC 60456:2010 Clothes washing machines for household use: methods for measuring the performance.

89.

UKCPI UK. I prefer 30, https://iprefer30.eu (2020, accessed 20 September 2020).