Standard layers — A new criterion of the thermal insulating properties of clothing

Abstract

A method of evaluating the thermal insulating properties of clothing on the basis of the number of so-called standard layers is described. Six typical kinds of clothing were chosen, made of fibres with similar permeability; for these types the thermal resistance was determined for dependence on the air velocity. These kinds of clothing were chosen as standard, as were their individual layers. In measurement of the total thermal resistance of the investigated clothing it is thus necessary to find the number of standard layers involved, i.e. the number of layers in the clothing and the difference of the individual layers from standard layers. The required value can then be read from a diagram or calculated from an equation. If Tg is very different from Ta (Tg-Ta > 10 K), a correction can be introduced using the diagrams. In contrast to use of the “clo” unit, the dependence of the thermal resistance on the air velocity is considered, as it was demonstrated that the boundary layer on the surface of the clothing moves inwards as a result of its permeability. The method is used successfully by the Hygienic Service of Czechoslovakia and in other socialist states.