Pilot studies of vapor transfer through breathable outerwear by simulating sweating in the cold

Claims that rainproof films allow the unimpeded evaporation of sweat have been examined by modifying a heat transfer method to include evaporation of water. This physical study simulates a casual hiker (2 mets) in 4 degrees C (40 degrees F) dry weather wearing clothing of 1.5-2.0 clo and sweating at 40 g X h-1. Goose down, wool, polyester, and polyolefin fills were combined with no protective cover, Gore-Tex, and polyurethane covers. No significant differences in insulation between dry (control) and wet (stabilized evaporation) occurred. Neither cover nor fill had significant effects on heat transfer. Total water evaporated (sweat produced) was affected only by the wool filler. A significantly greater amount of water was trapped by the natural fibers and the polyurethane cover. These data indicate that breathable rainwear is likely to have little effect on heat transfer, even though it allowed 89% of sweat to evaporate compared to 51% for the polyurethane raincoat.