Clothing thermal insulation during sweating

Heat transfer through clothing is an important topic related to thermal comfort in environmental engineering and functional clothing design. The total heat transmitted through clothing is commonly considered as the sum of the dry heat transfer and the evaporative heat transfer. Clothing thermal insulation measured in a nonperspiring condition, e.g., on a dry thermal manikin, is frequently used to calculate the dry heat transfer when the body is perspiring or even sweating heavily. The effect of perspiration on clothing thermal insulation with respect to dry heat transfer is not well understood, although it is widely speculated that perspiration reduces thermal insulation by wetting clothing assemblies. In this investigation, clothing thermal insulation with very low perspiration and very heavy perspiration is measured using a novel perspiring fabric thermal manikin. Clothing thermal insulation decreases during perspiration, and the amount of reduction varies from 2 to 8%, as related to water accumulation within clothing ensembles. This finding suggests the "after chill" effect of wearers after heavy exercise may not only be caused by heat absorption due to the desorption and evaporation of water within clothing, but also to reduced clothing thermal insulation. Also, for clothing that can absorb a large amount of moisture during sweating, clothing thermal insulation measured on dry manikins may need to be corrected when used for calculating dry heat loss (sometimes used for calculating moisture vapor resistance) on a sweating manikin and predicting thermal comfort during sweating.