The Limitations of Woodcock's "Moisture Permeability Index"

Abstract

The limitations of Woodcock's "Moisture Permeability Index, i_m ," are discussed together with his suggested method of measuring i_m. The general expression is derived for i_m. from which it is clear that the Moisture Permeability Index is not a dimensionless index but depends upon the values of the convective and radiative heat losses from the outer surface of the clothing assembly. It is pointed out that Woodcock's test method using an unheated sweating cylinder is liable to give an underestimate of the heat loss from a clothed, perspiring body, first because in actual wear the clothing may become wetted in which "liquid assisted heat and vapor transfer" will take place, and second, because evaporation tends to increase the convective heat transfer from the outer surface of the clothing.