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.Clothing thermal insulation is an important parameter in thermal comfort. It is used to determine the heat stress of a clothed person in a hot environment in terms of the required evaporation for thermal equilibrium, required sweat rate, and skin wetness (ISO 7933 [8], Parsons [ I3]), and to determine cold stress in a cold condition in terms of the required insulation (Holmer [6]). It is also an important measure of the effectiveness of clothing functional design and suitability of clothing systems (Mecheels and Umbach [ I 1 ]) for intended end uses.In the past, there has been considerable research on the effects of human physical activities and climatic conditions, (i.e., wind and surrounding temperature) on clothing thermal insulation (Lotens and Havenith [9], Holmer et al. [7], Havenith et al. [5], Sari and Berger [14], and Fan and Keighley [3]), but there has been comparatively little work on the effect of human perspiration on insulation. Consequently, clothing thermal insulation measured or predicted in nonperspiring (or dry) conditions is used to calculate the heat transfer through clothing when the body is perspiring (or sweating) with the possibility of error.

This paper reports on an experimental investigation of the effects of garment fit on clothing thermal insulation and moisture vapor resistance, both of which increase with the thickness of the air gap between the garment and the body when the air gap is small. The rate of increase gradually decreases as the air gap becomes thicker, and is much less than the theoretically ideal still air due to natural and forced convection. When the air gap exceeds a certain value, thermal insulation and vapor resistance may decrease with increases in the air gap. Thermal insulation and moisture vapor resistance reach a maximum at a certain air gap thickness depending on fabric properties, wind conditions, and garment fit. Tighter fitting garments are preferable to keep the body warm in windy conditions.

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The comfort of light-weight woven fabrics in the form of next-to-skin clothing is investigated by wear trials and the forearm test. The wear trial in neutral environmental conditions shows that light-weight wool and wool blend fabrics are generally less comfortable than the summer polyester, cotton poplin, and polyester/cotton, fabrics tested in this study. In terms of comfort, the main shortcoming of these light-weight wool fabrics is prickle. When the environmental temperature is high, especially when the body is sweating, the comfort of wool and wool blend fabrics is greatly reduced due to signifi cantly increased prickle. The forearm test in neutral environmental conditions shows that fabric-evoked prickle decreases with an increasing wool quality number, i.e., as the wool becomes finer. For light-weight wool and wool blend woven fabrics proddced from 70s quality and coarser wools, there is the potential problem of prickle when used as next-to-skin clothing materials.

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