Physiological evaluation of the resistance to evaporative heat transfer by clothing

Abstract

A new method has been developed to determine the ‘effective’ evaporative resistance of clothing in vivo. It is based on direct measurements of the water vapour pressure gradient between skin and ambient air and of the steady state rate of evaporative heat loss. Air is sampled by a system of tubes terminating at six different loci on the skin surface underneath clothing and pumped to an oxygen analyser via a mixing chamber. Water vapour pressure is derived from measurements of oxygen partial pressure in the atmospheric air using the general gas law. Evaporative heat loss is obtained from continuous weighing of the subject on an electronic balance, after correction for respiratory heat loss and metabolic weight loss. The technique was used to evaluate the heat transfer properties of two types of rainwear and an overall. A rainwear made of a new fabric (Gore-Tex) produced a significantly lower evaporative resistance than a rainwear made of traditional material (nylon). It is concluded that the present method, in combination with partitional calorimetry, enables a direct and simultaneous determination of the resistances of clothing to dry and humid heat loss for both resting and working subjects.