Factors Influencing Steady-State Heat and Water Vapor Transfer Measurements for Clothing Materials

Several techniques exist to evaluate the water vapor transport characteristics of clothing materials. The most common techniques include guarded hot plate sweating skin simulants and cup-type moisture vapor transmission rate tests. Theoretically, all such tests measure an identical property, water vapor resistance, but the results from different test methods rarely agree. The reasons for the discrepancies are the different conditions present in each test: in some cases the intrinsic properties of the materials are altered by the test conditions. The results of three studies illustrate important factors to be considered when evaluating the thermal and moisture vapor transport properties of textile materials. Each study concentrates on one particular aspect of the problems encountered in measuring relative performance characteristics of these ma terials. The first study involves an experimental correlation between two kinds of water vapor permeability tests. The second study looks at the influence of air per meability on heat and water vapor transport through woven and nonwoven fabrics. The final study determines the agreement between three different guarded hot plate (sweating skin simulant) test facilities that differ mainly in the air velocity over the test samples.