Formation mechanism of stickiness perception in dressed bodies under a hot environment: The effects of fabric properties,contact area,and skin wettedness

Abstract

Individuals often experience discomfort from their clothes sticking to them due to perspiration. The objective of this study was to elucidate the formation mechanism underlying this stickiness perception (SP). To this end, a series of wear trials were conducted involving various garments and activities within a controlled thermal environment. Measurements of contact area, subjective evaluations, and physiological responses were obtained. The results showed that the effects of fabric properties, contact area, and skin wettedness on SP were contingent upon the intensity of physical activity. The relationship between skin wettedness and SP was characterized by an exponential growth function. Skin wettedness served as a reliable predictor of SP in an unsaturated state. A significantly positive correlation was observed between contact area and SP under conditions of high skin wettedness. Additionally, the air permeability, surface roughness, water absorption capacity, and elongation of the fabric showed negative influences on stickiness perception during various activity phases, except for the rest phase. However, their association between fabric properties and stickiness perception may only be statistically significant. Therefore, it is necessary to conduct a more systematic investigation into the roles of fabric properties on stickiness perception. These insights can inform the optimized design of fabric configurations for summer garments, aiming to mitigate clothing discomfort associated with stickiness.

Keywords

Stickiness perception contact area fabric property skin wettedness wearing comfort

Introduction

In hot environments, garments frequently adhere to the skin due to perspiration, leading to increased friction or adhesive stimuli,^1,2 which result in a sensation of discomfort commonly referred to stickiness perception (SP).³ This feeling has been identified as a significant factor contributing to the discomfort experienced while wearing clothing in summer.^4,5 Consequently, a comprehensive understanding of the mechanisms underlying the formation of SP is crucial for enhancing clothing comfort.

In recent years, extensive research had been conducted to explore the influences of fabric properties and moisture on SP by studying the way that wet fabric rubbed or adhered to skin. Firstly, moisture has been identified as a critical factor in SP. The presence of moisture at the skin–fabric interface can lead to the softening and swelling of the skin, thereby increasing the actual contact area and the friction force between the skin and fabric.^6,7 Simultaneously, the accumulation of moisture can form liquid bridges between the fabric and skin, which enhances the adhesion force.⁸ Consequently, moisture can amplify the mechanical stimuli exerted by the fabric on the skin, leading to increased skin deformation and SP. The current research supports the assertion that a strong positive correlation exists between the water content of fabric and SP,⁹ as evaluated subjectively through assessments of wet fabric. Secondly, the water absorption capacity (WAC) of fabric significantly influences SP.^3,10 Specifically, a higher WAC enables the fabric to absorb and retain more water, thereby reducing the amount of water present at the skin-fabric interface, which in turn leads to a diminished SP. Tang et al. have identified a negative correlation between WAC and the absolute threshold of SP.¹¹ Similarly, Raccuglia et al. observed that an increase in WAC could attenuate SP.¹² Additionally, the surface features of the fabric should be considered critical in determining SP. A rough surface impedes the formation of a liquid bridge between the fabric and skin, resulting in decreased adhesion force and a weaker SP. However, this perspective lacks comprehensive support from existing studies. Tang et al. found that the plant-structured fabric with a rough surface exhibited a weak SP,¹¹ while no correlation was observed between SP and surface roughness (SMD) as measured by the Kawabata Evaluation System for fabric.¹³ These discrepancies in findings may be attributed to variations in research methodologies.

The aforementioned studies predominantly concentrate on the fabric level, with insufficient consideration given to clothing factors. Firstly, the clothing fit and body part involved significantly influence the contact area between the clothing and the body,¹⁴ thereby affecting the frictional or adhesive forces exerted by clothing on the skin, as well as SP. Secondly, the mode of mechanical stimulation exerted by clothing on the skin, as well as the mechanism of sweat loss, is contingent upon the individual’s activity level.¹⁵ For instance, during periods of rest, clothing may adhere to the body with no relative motion between the fabric and the skin. In such scenarios, sweat is primarily managed by the fabric’s ability to transfer moisture, while skin stimulation is predominantly influenced by static friction and adhesive forces. However, during physical activity such as running, clothing can intermittently adhere to or slide against the skin. Sweat loss mainly occurs through forced convection, while skin stimuli are predominantly influenced by dynamic friction and adhesion forces. Consequently, we propose that the impact of garment parameters on mechanical stimuli and sweat loss varies with activity levels, thereby affecting SP differently.

In light of the research background, the influence of fabric properties and clothing parameters on SP at varying activity levels has yet to be thoroughly examined. Furthermore, the applicability of conclusions regarding SP derived from fabric-level studies to actual clothing remained uncertain; and the relationship between moisture and stickiness perception had not been systematically quantified in clothing-level studies. Consequently, a series of wear trials were conducted to monitor physiological and perceptual responses. The objectives of this study were: (a) to investigate SP across different body parts and activity levels; and (b) to analyze the roles of skin wettedness, fabric properties, and contact area on stickiness perception at varying activity levels.

Methods

Participants

Eight healthy males (age 26 ± 1.3 years; height 173.63 ± 3.85 cm; body weight 63.37 ± 7.85 kg) volunteered to participate in this study. The participants had no history of cardiovascular disease, sensory-related disorders, or musculoskeletal injuries in the previous 12 months. They were given information about the purpose and procedure and signed informed consent.

Fabrics and Garments

Seven sets of summer suits, identical in design and size but varying in fabric, were selected for the study. Previous studies have found that stickiness perception is a subjective experience created in the human brain when wet clothing stimulates the skin through one or both modes of contact (friction and adhesion). Therefore, the friction and adhesion forces (or stimuli) of fabric against the skin are crucial factors that affect stickiness perception. At the fabric level, the influences of fabric properties on stickiness perception have been investigated under both friction and adhesion modes. Under the friction mode, researchers found that water absorption capacity and surface roughness are the primary factors affecting stickiness perception. Under the adhesion mode, researchers found that the surface roughness and air permeability played an important role on adhesion force, and the elongation of fabric have a certainly impact on adhesion distance (i.e. the maximum adhesion distance at which wet fabric separates from the skin surface). Therefore, we suggest that the main factors related to fabric that affect stickiness perception at the fabric level include water absorption capacity, surface roughness, air permeability, and tensile properties. To explore whether the conclusions regarding the influencing factors of stickiness perception obtained at the fabric level are also applicable at the clothing level, we selected seven types of fabrics commonly found in the market during the summer, each exhibiting significantly different water absorption capacity, surface roughness, air permeability, and tensile property, to use as experimental clothing fabrics. Fabrics COW, PESW, and SEW are plain-woven (W = woven) and made from different fiber types (CO = cotton, PES = polyester, SE = silk), commonly used to create summer shirts or pajamas. Fabrics COK, PESK, and PESELK are single-knitted (K = knitted) and made from different fiber types (CO = cotton, PES = polyester, and PES/EL = blending of polyester and elastane), commonly used to create summer T-shirts or yoga clothes. Fabric PA/ELK is a mesh-knitted fabric (PA/EL = blending of polyamide and elastane), commonly used to create summer sports garments. Each suit set comprised a short-sleeved T-shirt and a pair of shorts. The style and size of the garments are shown in Figure 1. Seven suit sets were named according to their fabric codes.

Figure 1.

Experimental garment style and size.

The thickness, weight, surface roughness, water absorption capacity, air permeability, and elongation of the fabric are summarized in Table 1. Surface roughness (SMD) denotes the texture of the fabric surface, which is quantified using the Kawabata Evaluation System.¹⁶ Water absorption capacity (WAC) refers to the maximum volume of water that a fabric can absorb, as determined by the methodology outlined by Tang et al.¹⁷ Air permeability (AP) represents the rate of airflow passing perpendicularly through a test specimen under specified test conditions of test area, measured in accordance with ISO 9237. Elongation (ELO) refers to the ratio of the extension of the test specimen to its initial length, as determined using a constant-rate-of-extension testing machine (INSTRON 3365) in accordance with ISO 20932. SMD and WAC affect the contact area between fabric and skin,¹⁸ as well as the water accumulation on the fabric surface, respectively, thereby influencing the friction force between fabric and skin. AP affects the trapped air at the fabric–skin interface,¹⁹ thereby influencing the adhesion force between the fabric and the skin. ELO affects the rate of change of the friction force between clothing and skin during body motion. Consequently, the fabric properties mentioned above may influence SP.

Table 1.

The specifications of fabrics

Fabric code	Fiber type	Structure	Thickness(mm)	Weight(g/m²)	SMD(µm)	WAC(g/m²)	AP(mm/s)	ELO
COW	100% CO	Plain	0.253	119.43	2.762	159.63	134.46	42.33%
PESW	100% PES	Plain	0.127	60.20	0.379	64.67	83.90	57.49%
SEW	100% SE	Plain	0.133	50.90	1.948	79.07	351.90	71.79%
COK	100% CO	Single jersey	0.525	175.67	3.879	381.53	437.58	162.78%
PESK	100% PES	Single jersey	0.346	105.47	3.666	224.20	2995.50	206.22%
PES/ELK	95% PES, 5% EL	Single jersey	0.573	193.73	3.373	405.03	490.16	448.36%
PA/ELK	78% PA, 22% EL	Mesh	0.533	181.43	6.960	250.67	1335.79	895.50%

Note. SMD = surface roughness; WAC = water absorption capacity; AR = air permeability; ELO = elongation; CO = cotton; SE = silk; PES = polyester; PA = nylon; and EL = elastane.

Experiment Design

The study was structured into two experiments: one aimed at measuring the contact area between the body and clothing, and the other focused on evaluating SP and physiological responses at varying activity levels in a hot environment.

Measurement of Contact Area

A 3D body scanner (Human Solutions GmbH, Germany) was employed to obtain highly precise three-dimensional (3D) images of the human body. Each participant was required to complete eight sets of 3D scanning tests, which included one test in a minimally clothed condition (wearing only underwear) and seven tests in various dressed conditions. The body posture, illustrated in Figure 2, necessitated that the big toe be aligned with a marker on the platform, with the arms slightly extended to the sides and secured with metal supports. This procedure aimed to ensure consistent body posture for each scan. Upon completion of all scans, the 3D scan data were post-processed using Geomagic Control 2015 (Geomagic, USA) to determine the contact area between the body and the clothing. The detailed post-processing steps were as follows:

The 3D scans were refined by eliminating scanning artifacts and covering any exposed body parts.

The 3D scans of the naked and dressed bodies were aligned using the uncovered body parts as reference.

The aligned body was segment into five regions: chest, abdomen, back, upper arm, and thigh.

The contact area for each body region was calculated. A ratio coefficient was introduced to quantify the contact area between the body and the clothing.¹⁴ The formula was as follows:

CA = A_{contact} / A_{covered}

(1)

where CA is the ratio coefficient; A_contact is the area that skin in direct contact with clothing; and A_covered is the area covered by clothing. The surface area of the body in contact with clothing was evaluated by measuring the distance between the surfaces of the naked body and the dressed body. If the distance was equal to the thickness of the fabric, the air gap thickness beneath the clothing was considered zero. Additionally, the uncertainties in the measurements needed to be accounted for, as they are comparable in magnitude to the fabric thickness. These included the inaccuracy (1 mm) of the 3D scans provided by the manufacturer of the 3D body scanner and the average alignment error resulting from the imperfect alignment of scans using uncovered body parts as the reference shapes. The average alignment error, as provided by the software for the uncovered body parts used as references, was 0.6 mm for the T-shirt and 0.5 mm for the shorts. Finally, we defined the sum of the uncertainties in the measurements and the fabric thickness as the distance at which the garment makes contact with the body. If the distance between the garment and the body equals this sum, the garment is considered to be in contact with the body.

Figure 2.

Body postures under the naked and dressed conditions: (a) Naked condition and (b) dressed condition.

However, we measured the contact area in a static state, which differed somewhat from the contact area measured in dynamic states (walking or running). Currently, the technology for real-time dynamic measurement of contact area between the body and garment is not yet mature, and similar studies have not been reported in the existing literature. Therefore, the limitations of this study may arise from the inadequacy of the measurement methods used. In the subsequent study, since the posture of the upper torso (chest, back, and abdomen) remains upright in both dynamic (walking or running) and static (sitting) states, we believe that the contact areas of these body parts should be similar in both states. Besides, during dynamic states, the arms and legs periodically swing back and forth, resulting in sinusoidal fluctuations in the contact area of these two parts. Therefore, the mean value of the contact area on both of these parts during dynamic states should be essentially the same as that in the upright posture. In summary, we suggest that the contact area of various parts of the human body can be roughly evaluated under dynamic conditions by measuring it in static conditions.

Thermal Response and Perception Evaluation

Experimental Protocol

Participants engaged in seven distinct groups of wearing trials conducted on separate days. During each trial, one of the seven sets of experimental garments was worn. The testing sequence was counterbalanced to mitigate any potential order effects, and all participants performed the trials at a consistent time each day to reduce circadian variation. Prior to each trial, the garments were equilibrated for 12 h in a thermally neutral chamber (25°C, 50% RH). The weight of each garment was measured using a digital scale with an accuracy of 0.1 g (SHIMADZU, Japan). Additional, participants were instructed to avoid strenuous exercise and abstain from caffeine and alcohol consumption for 12 h preceding the trial.

On the day of the experiment, participants initially arrived in a thermally neutral chamber and rested for 30 min to achieve physiological stabilization. During this acclimatization period, the participants’ height and weight were measured. Five iButtons (Maxim, San Jose, CA), which are sensors capable of monitoring both temperature and relative humidity,²⁰ were affixed to five specific skin sites (left chest, right abdomen, right back, left upper arm, and left thigh) to record local microclimate temperatures close to the skin and relative humidity at 1-minute intervals, as shown in Figure 3. The model number of the iButton is DS1923. Its measurement range for temperature and relative humidity is −20 to +85 °C and 0–100% RH, with a measurement accuracy of ±0.5 °C and ±5% RH. The central circular aperture of each iButton was positioned 2 mm from the skin surface. The microclimate temperature near the skin was presumed to be approximately equal to the temperature of the skin. Participants received instructions on how to use the SP scale and were guided in practice under the supervision and assistance of the experimenter. The SP scale (Figure 4) was designed according to Raccuglia’s study.²¹ The participants were asked to rate stickiness perception in the body parts where the iButtons were not attached. For example, the iButton was attached to the left chest, while the stickiness perception was evaluated on the right chest. After resting for 30 min, participants wore one set of experiment garments and arrived in a thermal environment (30°C, 50% RH). They were subsequently instructed to engage in a sequence of four activities: a 10-min rest, a 10-min walk, a 15-min run, and a 10-min recovery period. During the rest and recovery phases, participants were seated in a chair. During the walking and running phases, participants utilized a treadmill, maintaining speeds of 5 and 10 km/h, respectively. At 5-min intervals, participants were prompted to report their perceived stickiness rating for five specific body parts as well as for their whole body. The experiment procedure is illustrated in Figure 5.

Figure 3.

The measurement method of temperature and relative humidity on the skin surface.

Figure 4.

The rating scale of stickiness perception.

Figure 5.

The experiment procedure

Calculation of Skin Wittedness

Skin wettedness refers to the ratio between the evaporated heat flux from the body due to regulatory sweating and the maximum evaporative heat flux from the body for totally wet skin.²² Mean skin wettedness was calculated using following equation based on five measurement sites as used in the study of Houas and Ring.²³

\begin{matrix} W_{skin} = 0.07 \times W_{chest} + 0.175 \times W_{abdomen} \\ + 0.175 \times W_{back} + 0.19 \times W_{upperarm} \\ + 0.39 \times W_{thigh} \end{matrix}

(2)

Local skin wettedness (W_sk,i) was estimated for each body region based on Gagge’s study²⁴ and the equation derived by Fukazawa et al. The estimation was conducted as follows:

W_{sk, i} = \frac{q_{sw}}{q_{e max}} + 0.06 \approx \frac{P_{sk - i} - P_{a}}{P_{sks - i} - P_{a}}

(3)

where q_sw is the evaporated heat flux from the clothed body caused by regulatory sweating (W·m^-2); q_emax is the maximal evaporative heat flux from the body with the actual clothing and skin surface temperatures for completely wet skin (W·m^-2); 0.06 represents the skin wettedness due to skin diffusion (dimensionless); P_sk,i is the water vapor pressure at skin site i, kPa; P_a is the water vapor pressure in the air, kPa; and P_sks,i is the saturated water vapor pressure at skin site i calculated from skin temperature. The specific derivation process of equation (3) is detailed in Fukazawa’s research.²²P_a is calculated using the following equation:

P_{a} = R H_{a} \times P_{a, s}

(4)

where RH is ambient relative humidity, %; and P_a,s is saturated water vapor pressure in the air calculated from ambient temperature, kPa; P_a,s is calculated using the following equation:

P_{a, s} = 0.1 \times \exp (18.956 - \frac{4030.18}{T_{amb} + 235})

(5)

where T_amb is ambient temperature, °C. P_sk,i is expressed as:

P_{sks - i} = 0.1 \times \exp (18.956 - \frac{4030.18}{T_{sk - i} + 235})

(6)

where T_sk-i is skin temperature on measuring site i, °C. P_sk-i is expressed as:

P_{sk - i} = R H_{i} \times P_{sks - i}

(7)

where RH_i is the relative humidity of skin site i.

Statistical Analysis

In this study, the independent variables included fabric properties (specifically SMD, WAC, AP, and ELO), contact area, and skin wettedness, while the dependent variable was SP. The data on skin wettedness, skin temperature, contact area, and SP of eight subjects were presented as means ± standard deviation. The Shapiro–Wilk test was used to assess the normal distribution of the data. To examine the effects of garments and body regions on contact area, skin temperature, skin wettedness, and SP, a non-parametric Kruskal–Wallis (K-W) test was conducted. Additionally, Pearson correlation analysis was utilized to explore the relationships between fabric properties, contact area, and SP. Exponential growth function was used to elucidate the relationship between skin wettedness and SP. Linear regression was conducted to evaluate the predictors of SP. A significance threshold of p < 0.05 was applied in all statistical analyses. Data were processed using the commercial software IBM SPSS 22.0.

Results

Contact Area

The Shapiro–Wilk test indicated that the contact area data do not follow a normal distribution (p < 0.01); therefore, the non-parametric K-W test was used to analyze the differences in the contact area of various body parts or garments. As shown in Figure 6, the contact areas on the chest and back are significantly greater than those on the upper arms and thighs (p < 0.01), and the contact areas on the uppers and thighs are significantly greater than those on the abdomen (p < 0.05). In the garments, no significant differences in the contact area are observed among the seven items. Nevertheless, the four knitted garments (indicated in blue) generally exhibit larger contact areas on the chest compared to the three woven garments (indicated in red).

Figure 6.

The means and standard deviation of contact area of eight subjects. ** and *: significant difference (p < 0.01) and (p < 0.05), respectively; and NS: no significant difference.

Skin Temperature and Skin Wettedness

Figures 7 and 8 depict skin temperatures and skin wettedness on five local body parts across seven different garments during various activities. Overall, the skin temperature exhibits an initial increase during rest, followed by stabilization, a decrease during running, and a subsequent increase during recovery. During running and recovery, the skin temperature on the chest is observed to be comparatively lower than that of other body parts. These results align with the previous research in the field.²⁵ This phenomenon can be attributed to the increased production of sweat on the chest, which enhances heat dissipation through evaporation and subsequently leads to a decrease in skin temperature.²⁶ Additionally, no significant differences in skin temperature are observed among the various garments.

Figure 7.

Skin temperatures on the local body parts across various activities. (a) Rest; (b) walking; (c) running; and (d) recovery.

Figure 8.

Skin wettedness on the local body parts across various activities. (a) Rest; (b) walking; (c) running; and (d) recovery. *Significant difference (p < 0.05).

The skin wettedness on five local body parts shows an initial increase, followed by stabilization throughout the course of the experiment. Notably, considerable variations in skin wettedness are observed across the five body parts examined, with the chest and back displaying relatively higher levels compared to the thigh. These results align with previous research on the distribution of sweating during moderate physical activity,²⁶ suggesting consistent patterns in physiological responses. Furthermore, disparities in skin wettedness are noted among the different garments during rest and walking. The skin wettedness on the back in garment COK is significantly higher than that in garment PEK (p < 0.05).

Stickiness Perception

Figure 9 shows SPs for both local and overall body parts. The SP first increased and then decreased throughout the experiment. During rest and walking, there is no significant difference in SPs across various local areas, while during running and recovery, SPs on the chest and back are relatively higher than those on the thigh. Additionally, there are no significant differences in SPs among different garments during rest and walking, while SPs in woven garments (indicated in red) are generally higher than those in knitted garments (indicated in blue) during both running and recovery. Especially during walking, garments SEW and PEW on the chest and back exhibit a significantly higher SP than garments PEK (p < 0.05).

Figure 9.

Stickiness perceptions on the local and overall body parts across various activities. (a) Rest; (b) walking; (c) running; and (d) recovery. *Significant difference (p < 0.05).

Influencing factors of stickiness perception

Relationships Between Fabric Properties and SP

As demonstrated in Table 2, no significant correlations were identified between SP and fabric properties during rest and walking. However, during running, significant negative correlations were observed between SMD and SPs on the abdomen, back, upper arm, and overall body; between AP and SPs on the chest, abdomen, back, upper arm, and overall body; and between ELO and SPs on the upper arm. Additionally, during the recovery phase, significant negative correlations were noted between WAC and SPs on the back and overall body, as well as between AP and SPs on the chest, abdomen, and overall body. Among these correlations, SMD had the highest correlation with SP on the upper arm during running, WAC had the highest correlation with SP on the back during recovery, and AP had the highest correlation with SP on the chest during running. However, ELO only correlated with SP on the upper arm during running.

Table 2.

Correlation coefficients between stickiness perception and fabric parameters across various activities.

Correlation coefficient (r)		Stickiness perception
Fabric property	Activity	Overall	Chest	Abdomen	Back	Upper arm	Thigh
SMD	Rest:	0.018	−0.145	−0.519	−0.487	−0.433	0.019
	Walking	0.108	0.036	0.036	−0.108	−0.464	0.164
	Running	−0.786*	−0.714	−0.757*	−0.775*	−0.786*	−0.378
	Recovery	−0.667	−0.643	−0.679	−0.704	−0.643	−0.371
WAC	Rest:	0.291	0.346	−0.445	−0.144	0.059	0.412
	Walking	0.342	0.429	0.360	0.270	0.036	0.436
	Running	−0.643	−0.750	−0.613	−0.721	−0.607	−0.126
	Recovery	−0.775*	−0.750	−0.714	−0.852*	−0.643	−0.037
AP	Rest:	−0.109	−0.018	−0.334	−0.505	−0.374	−0.206
	Walking	−0.324	−0.357	−0.378	−0.450	−0.500	−0.273
	Running	−0.893**	−0.929**	−0.883**	−0.995**	−0.857*	−0.577
	Recovery	−0.829**	−0.786*	−0.857*	−0.704	−0.714	−0.482
ELO	Rest:	−0.430	−0.232	−0.696	−0.634	−0.683	0.086
	Walking	−0.130	−0.293	−0.242	−0.499	−0.483	−0.010
	Running	−0.580	−0.600	−0.625	−0.629	−0.830*	−0.511
	Recovery	−0.653	−0.472	−0.615	−0.466	−0.286	−0.175

Note. SMD = surface roughness; WAC = water absorption capacity; AP = air permeability; and ELO = elongation. *, ** Significant correlation (p < 0.05 and p < 0.001, respectively).

Relationship Between Contact Area and SP

Figure 10 shows the relationships between contact area and stickiness perception on various local body parts across different activities. Each small graph in Figure 10 consists of 35 data points, with the horizontal axis representing the contact area and the vertical axis representing the stickiness perception (7 garments ×5 local body parts). The significant positive correlations between contact area and SP across various activities were observed (all p-values < 0.05). Based on the linear analysis results, the woven garments (indicated in red) exhibit higher slopes and intercepts compared to the knitted garments (indicated in blue) across various activities, and the slopes of the linear functions during running and recovery are significantly steeper than those observed during rest and walking, nearly twice as steep. This suggests that the woven garments are more likely to perceive stickiness compared to the knitted garments in the same contact area, and the role of contact area on SP during running and recovery is more significant than during rest and walking.

Figure 10.

Relationships between stickiness perception and contact area on various local body parts across different activities. (a) Rest; (b) walking; (c) running; and (d) recovery.

Relationship Between Skin Wettedness and SP

The relationships between skin wettedness and SPs on both local and overall body regions are illustrated in Figure 11. The contact areas of different garments on the same body part are similar (Figure 6), which helps to minimize the interference of contact area when investigating the influence of skin wettedness on SP. In general, when skin wettedness is below 0.6, SP remains minimal (<3, slight stickiness) and relatively constant; however, when skin wettedness exceeds this threshold, SP begins to increase, and once skin wettedness surpasses 0.9, SP shows a rapid increase. The relationships between skin wettedness and SPs were fitted using an exponential growth function as follows:

S P_{i} = S P_{0 - i} + a_{i} \times (\frac{w_{i} - w_{0 - i}}{t_{i}})

(8)

where SP is stickiness perception; w is skin wettedness; SP₀, w₀, t, and a are the offset, center, growth constant, and amplitude of exponential growth function; i is the body part. The fitting functions and the coefficients of determination (R²) for the local body parts and the overall body are summarized in Table 3. SP₀ and t represent the initial intensity and the growth rate of stickiness perception produced by skin wettedness, respectively. A higher value of y₀ indicates a greater likelihood of perceiving stickiness, whereas a lower value of t indicates a faster growth rate of SP. Table 3 revealed that the back exhibited a higher initial intensity and a more rapid growth rate of SP, in contrast to the thigh, which demonstrated a lower initial intensity and a slower growth rate.

Figure 11.

Relationships between skin wettedness and stickiness perceptions on the local body parts and the overall body. (a) Chest; (b) abdomen; (c) back; (d) upper arm; (e) thigh; and (f) overall body.

Table 3.

Exponential growth functions and coefficients of determination (R²) for the local body parts and the overall body.

Body part	Exponential growth function				R ²
Body part	SP₀	W₀	a	t	R ²
Overall	−0.845	−2.991	9.973*10^-6	0.289	0.807
Chest	0.329	0.311	0.082	0.143	0.824
Abdomen	−0.392	−0.050	0.053	0.207	0.754
Back	0.539	0.323	0.010	0.098	0.823
Upper arm	−0.520	−0.492	0.047	0.302	0.789
Thigh	−3.156	−3.649	0.017	0.748	0.741

Predictors of SP

A multiple stepwise regression analysis was performed to examine the predictors of SP across various activities (rest, walking, running, and recovery). Fabric properties (WAC, AP, SMD, ELO), skin wettedness, and contact area were designated as independent variables, while SP served as the dependent variable. As illustrated in Table 4, skin wettedness emerged as the most significant predictor of SP during rest, walking, and running, with its influence waning during the recovery. Additionally, contact area was found to be particularly crucial for SP, especially during recovery. Among the fabric parameters, ELO was identified as a key factor influencing SP during rest, walking, and running. Additionally, AP significantly affects SP during walking, running, and recovery. In contrast, the impacts of SMD and WAC on SP are relatively small, with SMD having a slight influence during running and WAC during recovery.

Table 4.

Coefficient of determination (R²) in regression model across various activities

R ²	W_skin	CA	WAC	AP	SMD	ELO
Rest	0.536	—	—	—	—	—
Walking	0.643	0.060	—	0.053	—	0.023
Running	0.502	—	—	0.115	0.031	—
Recovery	0.191	0.115	0.086	0.052	—	—

Note: W_skin = skin wettedness; CA = contact area; WAC = water absorption capacity; AP = air permeability; ELO = elongation; and SMD = surface roughness.

It is important to note that, in the analysis above, some of the significant associations between SP and fabric properties, SP and contact area, and SP and skin wettedness may be accidental and lack practical significance. Therefore, a more in-depth analysis of the impact of these factors on SP was conducted in the “Discussion” section.

Discussion

The aim of this study was to investigate the effects of fabric properties, contact area, and skin wettedness on stickiness perception. To achieve this objective, we examined the contact area, skin wettedness, and SPs of different garments across various body parts. The outcomes indicated that the effects of these factors on SP are contingent upon the level of human activity.

Effects of Fabric Properties

The primary objective of this study was to investigate whether the findings observed at the fabric level were applicable to clothing as a whole. At the fabric level, WAC was noted to have a substantial impact on SP.⁹ The fabric with a higher WAC demonstrated an increased ability to retain water its structure, thereby reducing the amount of water present between the fabric and the skin, which in turn diminished the perceived stickiness. However, this conclusion drawn at the fabric level was not fully corroborated by the findings of the study. Our investigation revealed that the influence of fabric properties, including WAC, on SP was contingent upon the state of physical activity of the human body, as shown in Tables 2 and 4 and Figure 11.

During the period of rest, no significant correlation was observed between SP and various fabric properties. This lack of correlation can be attributed to the minimal perspiration experienced by participants during rest. Figure 8 shows lower skin wittedness under different garments (mean skin wettedness < 0.67). At the fabric level, previous studies have indicated that, under conditions of no water, the influence of various fabric properties on the friction force between the fabric and the skin is not significant,^6,27,28 and the friction force is unlikely to change significantly with variations in the properties of the fabric; while moisture appears on the skin’s surface, the friction force between the fabric and the skin shows a significant spike. Moreover, moisture is essential for creating an adhesion force between the fabric and the skin. If no moisture is present, adhesion force is nearly zero, regardless of changes in the fabric properties. It can be observed that when skin wettedness is low, the friction or adhesion force between the skin and clothing is minimal, irrespective of the fabric properties. Consequently, the fabric properties did not significant impact SP under these conditions.

During walking, AP and ELO had a slight impact on SP, as illustrated in Table 4; however, both of these fabric properties showed no significant correlation with SP, as indicated in Table 2. The motion induced forced convection within the air gap between the body and the clothing. Initially, we hypothesized that an increase in AP would facilitate the exchange of water vapor between the internal and external environments of clothing, thereby reducing moisture accumulation on the skin surface and consequently contributing to a reduced friction force. However, no significant difference in skin wettedness was observed among the different garments (p > 0.05), as illustrated in Figure 8. This suggests that the variation in AP among these garments did not lead to a significant difference in skin wettedness during this period. Consequently, the aforementioned explanation did not appear to be valid. From a second perspective, we propose that intermittent adhesion stimuli form the garment on the skin may occur due to motion. Higher AP can result in a reduction in the pressure difference between the trapped air at the fabric–skin interface and the external air,²⁹ thereby decreasing the adhesion force between the fabric and the skin, and consequently weakening adhesion stimuli and SP. Similarly, the fabric with a higher ELO contributed to a reduction in the friction force exerted by clothing on the skin, which was attributable to fabric stretch deformation during walking. This, in turn, had a negative influence on SP. However, the analysis from the second perspective is still speculative, as walking also produces frictional stimuli from the garment against the skin. Nevertheless, we did not observe the effect of SMD on SP (Tables 2 and 4). Likewise, the effect of ELO on SP was also inconsistent between the walking and running stages. To sum up, the existing results are not sufficient to clarify the relationship among SP, AL and ELO; therefore, more experimental studies should be conducted to elucidate this relationship.

During running, AP had a significant influence on SP, as shown in Table 2. Moreover, the skin wettedness of various garments had no significant difference, as shown in Figure 8. Therefore, we presume that AP does not affect SP by affecting skin wettedness. The primary influence of AP was on the adhesion force between the skin and the fabric. During the running stage, a significant amount of sweat accumulates on the chest and back, creating a large adhesion area between the skin and the clothing in these parts. Under the conditions of high adhesion area and increased sweat, AP significantly reduces the adhesion force between the fabric and the skin, thereby alleviating SP in these areas. Therefore, AP exhibited a more pronounced impact on SP in these regions. Furthermore, since SMD predominantly affected the friction force between the skin and fabric, and the upper arm was more active region during running, SMD demonstrated a significant impact on SP in the upper arm. Additionally, under conditions of high skin wettedness, a rougher fabric surface was less conducive to the formation of a liquid bridge between the fabric and the skin, resulting in reduced friction and adhesion forces, which were associated with diminished SP. Therefore, SMD had a negative impact on SP in the upper arm due to its active role during running. However, compared to the walking phase, the effect of SMD on SP was not clarified, which may be attributed to lower skin wettedness during that stage. Moreover, the results of SMD analysis in Tables 2 and 4 were still inconsistent. Therefore, the impact of SMD on SP may only be a correlation in the data. Future discussions should focus on the relationship between both under high skin wettedness.

During the recovery phase, intermittent stimuli (dynamic friction) from the garment on the skin were less likely to occur in a sedentary state. However, the SMD and ELO mainly affected dynamic friction force from the garment on the skin during the activities of one subject. Therefore, the effects of SMD and ELO on SP are not significant. The correlations between SMD and SP as well as between EL and SP were diminished. Conversely, when the subject was in a sedentary state, the garment adhered more easily to the skin. The fabric with a higher WAC absorbed more moisture from the skin surface, thereby reducing the friction and adhesion forces exerted by the clothing on the skin, which in turn weakened SP. Therefore, a significant negative correlation was found between SP and WAC in Table 2. In a similar way, given the larger adhesion area on the back, WAC significantly influenced SP in this region. This may be a speculation for the significant negative correlation between WAC and SP. Of course, more experimental studies should have been conducted to test our hypotheses. Furthermore, as shown in Tables 2 and 4, AP and SP are significantly negatively correlated. In a static state, the garment easily adheres to human skin. The high AP can enhance airflow across the inner and outer surfaces of the fabric, thereby reducing the adhesion between the fabric and the skin. This causes the wet fabric to detach from the skin, reducing the stickiness perception. Therefore, we speculate that it is reasonable that AP has a negative impact on SP during the recovery phase.

Effect of Contact Area

The other study aimed to investigate the effect of contact area on SP. To achieve this objective, we examined the relationship between contact area and SPs in different body parts across various activities. Figure 11 illustrates significant positive correlations, particularly pronounced during running and recovery phases. This phenomenon can be attributed to the increase in the friction and adhesion forces between the body and the clothing as the contact area expends, thereby enhancing SP. However, Raccuglia et al. investigated the stickiness perception under clothing made from fabrics with three different mesh types and found that the stickiness perception under clothing made from fabric with large meshes was stronger than that of fabric with small meshes.¹⁵ They explained the abnormal variation between stickiness perception and contact area by referencing the inverse relationship between the size of the fabric mesh and its water absorption capacity. They suggested that although the contact area of clothing with large mesh is small, the capacity of the clothing to absorb water is also reduced, resulting in higher skin wettedness on the skin surface. Therefore, the stickiness perception is enhanced by skin wittedness. Conversely, in the present study, skin wettedness across the same body regions was found to be consistent. Therefore, the exclusion of moisture interference facilitated a more confirmation that the contact area had a positive effect on SP. Moreover, as illustrated in Figure 10, the slopes of the functions are greater during both the running and recovery phases, and the slopes and intercepts are higher in the woven fabrics (indicated in red) across the four activities. This phenomenon was further indicated that the skin wettedness, contact area, and fabric properties interact to influence the stickiness perception.

Effect of Skin Wettedness

In this study, various activity states were established to induce a nearly linear increase in skin wettedness with the objective of thoroughly examining the relationship between skin wettedness and SP. To the best of our knowledge, this specific quantitative relationship has not been previously documented in the literature. Consequently, we initially established an exponential growth function to describe the relationship between skin wettedness and SP. As shown in Figure 11, our finding revealed that when skin wettedness was below 0.6, changes in fabric properties and contact area had minimal impact on SP. This suggests that a certain level of skin wettedness was a prerequisite for the manifestation of SP. Therefore, maintaining skin wettedness below 0.6 can effectively avoid SP, regardless of the type of garments worn. However, when skin wettedness was over 0.6, SP increased rapidly with rising skin wettedness due to the accumulation of moisture on the skin surface, which enhanced friction and adhesion forces, thereby intensifying SP. Once skin wettedness reached saturation, its influence decreased, and the fabric properties and garment parameters became more significant. This may be due to a lack of sensitivity in characterizing the amount of sweat on the skin surface when the skin wettedness is near or at saturation. In other words, when skin wettedness approaches one, it becomes difficult to change the skin wettedness even if the amount of sweat continues to increase. This results in a weakened influence on stickiness perception. Therefore, in the future, it is necessary to propose indicators that can more accurately describe the amount of sweat on the skin surface, allowing for a clearer study of the mechanisms behind stickiness perception under clothing. Of course, regardless of the specific conditions, skin wettedness serves as a reliable predictor of SP in an unsaturated state. Moreover, since the back skin had a larger contact area with the garment (Figure 6), it contributed to greater friction and adhesion forces in this region, resulting in a more noticeable stickiness perception (Figure 5c) as skin wettedness increased.

Conclusions

In the study, a series of wear trials in a hot environment were conducted, and the SPs and physiological responses were recorded in real time. The main aim was to investigate the effects of fabric properties, contact area, and skin wettedness on SP across various activities. The key findings were as follows:

(1)Previous research identified WAC as the primary determinant of SP at the fabric level. However, this conclusion does not fully extend to wearing conditions. Our study demonstrates that the influences of fabric properties and contact area on SP depended on the state of physical activity, encompassing variations in skin wettedness and body motion. During the recovery phase, the WAC negatively affects SP because the fabric attached to the skin can absorb a significant amount of perspiration. The AP, SMD, and ELO showed a negative influence on SP during various activity phases, except for the rest phase. However, our current findings are insufficient to fully explain the mechanisms of their influence on stickiness perception, and their association may be statistically significant but not necessarily meaningful. Nevertheless, based on the available research results, we still believe that the fabric, which has a rough surface, a high air permeability, stretch elasticity, and water absorption capacity, helps weaken SP.

(2)When skin wettedness was below 0.6, SP remained minimal and relatively constant, irrespective of fabric parameters and contact area; when skin wettedness exceeded this threshold, SP rapidly increased with further increments in skin wettedness; and when skin wettedness approached one, its impact on SP would decrease. Skin wettedness served as a reliable predictor of SP in an unsaturated state.

(3)The contact area had a positively influence on SP during both the running and recovery phases. A larger contact area helps to increase the friction and adhesion forces between the clothing and the skin, thereby enhancing SP. For example, the back region exhibited a heightened susceptibility to perceiving stickiness, attributable to its larger contact area.

In the future, it is necessary to conduct a systematic investigation into the roles of fabric properties on SP in different local body regions across various activities. This will offer a more comprehensive explanation of how fabric properties influence the stickiness perception. Moreover, it will facilitate optimized design of fabric configurations for summer garments tailored to specific occupational contexts, thereby alleviating discomfort from stickiness.

Footnotes

Acknowledgements

The authors thank the members of the Key Laboratory of Clothing Design & Technology, Donghua University and all the volunteers who participated in the wearing trial for their support.

Declaration of conflicting interests

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

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Xi'an Polytechnic University Doctoral Scientific Research Initial Fund Project (BS202310).

ORCID iDs

Rongfan Jiang

Jian Li

References

Lou

Xie

, et al. Simulating adhesion of wet fabrics to water: gravity of liquid bridge-based theoretical model and experimental verification. Textil Res J 2016; 87(7): 769–779.

Gerhardt

Lenz

Spencer

, et al. Skin–textile friction and skin elasticity in young and aged persons. Skin Res Technol 2009; 15(3): 288–298.

Tang

KPM

Chau

Kan

, et al. Magnitude estimation approach for assessing stickiness sensation perceived in wet fabrics. Fiber Polym 2018; 19(11): 2418–2430.

Kamalha

Zeng

Mwasiagi

, et al. The comfort dimension: A review of perception in clothing. J Sens Stud 2013; 28(6): 423–444.

Wang

Zhang

, et al. Effects of inner and outer clothing combinations on firefighter ensembles’ thermal- and moisture-related comfort levels. J Text I 2013; 104(5): 530–540.

Kenins

Influence of fiber type and moisture on measured fabric-to-skin friction. Textil Res J 1994; 64: 722–728.

Derler

Gerhardt

Lenz

, et al. Friction of human skin against smooth and rough glass as a function of the contact pressure. Tribol Int 2009; 42(11-12): 1565–1574.

Qiu

Xie

, et al. A novel testing method of the wet wearing comfortability of fabrics. Advanced Materials Research 2013; 627: 476–479.

Tang

Chau

Kan

, et al. Assessing the accumulated stickiness magnitude from fabric–skin friction: Effect of wetness level of various fabrics. Roy Soc Open Sci 2018; 5(8): 180860–180878.

10.

Tang

KPM

Chau

Kan

, et al. Instrumental evaluation of stickiness of textiles under wet skin surface. IEEE Access 2018; 6: 24777–24792.

11.

Tang

KPM

Kan

Fan

JT.

Psychophysical measurement of wet and clingy sensation of fabrics by the volar forearm test. J Sens Stud 2015; 30(4): 329–347.

12.

Raccuglia

Pistak

Heyde

, et al. Human wetness perception of fabrics under dynamic skin contact. Textil Res J 2017; 88(19): 2155–2168.

13.

Jiang

Wang

YY.

Study of the human stickiness perception of wet fabric on the volar forearm via two contact modes: Friction and adhesion-separation. Perception 2020; 49(12): 1311–1332.

14.

Psikuta

Frackiewicz

Frydrych

, et al. Quantitative evaluation of air gap thickness and contact area between body and garment. Textil Res J 2012; 82(14): 1405–1413.

15.

Raccuglia

Sales

Heyde

, et al. Clothing comfort during physical exercise – determining the critical factors. Appl Ergon 2018; 73: 33–41.

16.

Kawabata

Niwa

Objective hand measurement of nonwoven fabrics part I: Development of the equations. Textil Res J 1994; 64: 597–610.

17.

Tang

KPM

Kan

Fan

JT.

Assessing and predicting the subjective wetness sensation of textiles: Subjective and objective evaluation. Textil Res J 2014; 85(8): 838–849.

18.

Wang

Liu

Wang

FM.

Fabric–skin friction property measurement system. Int J Cloth Sci Tech 2010; 22(4): 285–296.

19.

Pailler-Mattéi

Zahouani

Analysis of adhesive behaviour of human skin in vivo by an indentation test. Tribol Int 2006; 39(1): 12–21.

20.

Gerrett

Redortier

Voelcker

, et al. A comparison of galvanic skin conductance and skin wettedness as indicators of thermal discomfort during moderate and high metabolic rates. J Therm Biol 2013; 38(8): 530–538.

21.

Raccuglia

Hodder

Havenith

Human wetness perception in relation to textile water absorption parameters under static skin contact. Textil Res J 2017; 87(20): 2449–2463.

22.

Fukazawa

Havenith

Differences in comfort perception in relation to local and whole body skin wettedness. European Journal of Applied Physiology 2009; 106(1): 15–24.

23.

Filingeri

Fournet

Hodder

, et al. Tactile cues significantly modulate the perception of sweat-induced skin wetness independently of the level of physical skin wetness. J Neurophysiol 2015; 113(10): 3462–3473.

24.

Gagge

A new physiological variable associated with sensible and insensible perspiration. Am J Physiol 1937; 120: 277–287.

25.

Wong

ASW

Yeung

PKW.

Predicting clothing sensory comfort with artificial intelligence hybrid models. Textil Res J 2004; 74: 13–19.

26.

Smith

Havenith

Body mapping of sweating patterns in male athletes in mild exercise-induced hyperthermia. Eur J Appl Physiol 2011; 111(7): 1391–1404.

27.

Gwosdow

Stevens

Berglund

, et al. Skin friction and fabric sensations in neutral and warm environments. Textil Res J 1986; 56: 574–580.

28.

Gerhardt

Strassle

Lenz

, et al. Influence of epidermal hydration on the friction of human skin against textiles. J R Soc Interface 2008; 5(28): 1317–1328.

29.

Pailler

Zahouani

Study of adhesion forces and mechanical properties of human skin in vivo. J Adhes Sci Technol 2004; 18(15–16): 1739–1758.