| Abstract |
Military uniform materials vary widely in their heat transfer and water vapor transport characteristics. In hot environments the water vapor permeability of clothing should be high to maximize evaporative cooling. High water vapor permeability is also important in cold environments to prevent or minimize water buildup in clothing. 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 (MVTR) tests. Theoretically all such tests measure an identical property, water vapor resistance, but the results between different types of tests rarely agree. The reasons for the discrepancies are due to the the different conditions present in each test; in some cases the intrinsic properties of the materials are altered by the test conditions. MVTR and sweating skin simulant water vapor resistances correlate quite well for permeable woven and nonwoven textile materials. Semipermeable membranes divide neatly into two types of behavior. Hydrophobic membranes show good correlation between MVTR and sweating skin simulant tests, but hydrophilic membranes show poor agreement between the two types of tests. The scatter is accounted for by noting the different vapor p re gradient present in the two types of tests, which, when combined with the different levels of water present in the hydrophilic membranes, drastically alters the intrinsic transport characteristics of these hydrophilic membranes. The implications for materials screening testing am discussed. Water Vapor Permeable Materials, Thermal Insulation, Heat Transfer, Evaporative Cooling, Water Vapor, Heat Stress (Physiology), Vapor Permeation, Dif |
