Evaporative Heat Loss and Clothing

Several experiments have been conducted on the effect of clothing on evaporative heat loss. 1) The movement of sweat from production to evaporation was observed in nude subjects, on subjects wearing underwear and underdrawers, and on subjects wearing two layers of clothing during a two-hour heat exposure period. The percentage of evaporated sweat was found to be inversely proportional to total sweat loss. When this relation was taken into consideration, it was revealed that the percentage of evaporated sweat was smaller if more layers of clothing were added, or if water-proof or vapor-proof materials were added. 2) Using a so-called "sweating cylinder," the cooling power of water dissipated from the surface of the cylinder was measured when the cylinder was covered with one, two, or three layers of various kinds of cloths. The cooling efficiency (actual evaporative cooling/latent heat of total water lost) was about 95% when the cylinder was uncovered. As more layers of covering cloth were added, the cooling efficiency became less. When the covering cloth touched the wet surface of the cylinder directly and absorbed water, the cooling efficiency was remarkably reduced because a large portion of the water absorbed in the cloth remained unevaporated.