Dynamic moisture permeation through clothing.

Dynamic moisture permeation through clothing often occurs during thermal transience, causing an imbalance between evaporative heat loss from the skin (Esk) and that from the clothing surface (Ecl). A device was designed to observe Esk and Ecl simultaneously. It consists of two relative humidity sensors coupled with thermistors so that densities of water vapor at two points within the boundary layer can be calculated. The rate of local evaporation is then estimated from Fick's law of diffusion. Local evaporation rates from the skin and clothing surface at the chest, arm, and thigh were measured during exposure to controlled ambient temperatures varying from 20 degrees-40 degrees C. The subjects wore four different types of helicopter pilot suits: Nomex/Neoprene, Goretex, cotton ventile, and Nomex/Insulite. For the Goretex and cotton ventile suits, consisting of relatively permeable and hygroscopic fabrics, a sudden increase in Esk, exponential decay of Esk, and a gradual increase in Ecl were observed. These appear to be associated with, respectively, the onset of sweat secretion, moisture build-up within the clothing, and water gain in the fabric. Thus, the device may be useful for observing dynamic moisture permeation through clothing.