PHYSICAL TECHNIQUES FOR DETERMINING THE RESISTANCE TO HEAT TRANSFER PROVIDED BY CLOTHING

It is necessary to quantify the thermal insulation and evaporative resistance properties of clothing systems so that the heat exchange between the body and the environment can be determined and a person's performance in that environment can be predicted using biophysical models. This paper reviews the physical methods for directly measuring resistance data on fabrics and clothing ensembles and discusses problems associated with different techniques. In addition, methods for estimating the resistance values for clothing from different fabric and clothing properties will be mentioned. FABRICS The resistance to dry heat transfer (i.e., insulation) can be measured using the rate of cooling method, the constant temperature method (e.g., guarded hot plate), and heat flow meter. Flat plate instruments or cylinders have been used, with each type having advantages and disadvantages over the other. Fabric insulation can be estimated from thickness, so the compressometer, micrometer, and pendulum methods will be discussed. The evaporative resistance of fabrics can be measured using a sweating hot plate device or cylinder. A liquid barrier of known resistance is needed to keep the fabric dry during the test. Measurements can be made with and without a temperature gradient between the hot body and the environment. Other methods for measuring the diffusion of water vapor through a fabric include the ASTM control dish method and the Canadian DND apparatus. [1-10