Thermal resistance behaviour of single and multiple layers of clothing fabrics under mechanical load

The thermal resistances of clothing assemblies comprising up to eight dry layers, in series, of a single fabric (either woven cotton, polyester or nylon) in air at atmospheric pressure have been measured and compared with other materials. Application of a compressive loading led typically to the resistance of a stack of eight polyester cloth layers falling from 46 x 10-3 Km2 W-1 under zero loading to 32 x 10-3 Km2 W-1 under 31 Nm-2. The percentage reduction in resistance for an additional equal increment of loading would be considerably smaller. Under load, the thermal behaviour of multiple layer assemblies is identical to that of a single layer of the same material and overall thickness and so it was concluded that contact resistances between successive layers are usually of secondary importance for clothing fabrics in air at atmospheric pressure and that the insulation provided by such an assembly is primarily dependent upon the volume of air held stagnant within the matrix, provided that no thermal radiation [`]windows' are present.