4.1 The thermal resistance, evaporative resistance, and total heat loss provided by fabrics, films, coatings, foams, and leathers, including multi-layer assemblies, is of considerable importance in determining their suitability for use in fabricating protective clothing systems.

4.1.1 The thermal resistance, evaporative resistance, and total heat loss can be significantly affected by environmental conditions. Extreme care must be taken when using results measured under standard testing conditions to determine a material's suitability for use in conditions outside the testing conditions.

4.2 The thermal interchange between people and their environment is an extremely complicated subject that involves many factors in addition to the steady-state resistance values of fabrics, films, coatings, foams, and leathers, including multi-layer assemblies. Therefore, thermal resistance values, evaporative resistance values, and total heat loss measured on a hot plate may or may not indicate relative merit of a particular material or system for a given clothing application. While a possible indicator of clothing performance, measurements produced by the testing of fabrics have no proven correlation to the performance of clothing systems worn by people. Clothing weight, drape, tightness of fit, and so forth, can minimize or even neutralize the apparent differences between fabrics or fabric assemblies measured by this test method.

4.3 The thermal resistance and evaporative resistance of clothing systems and items can be measured with a heated sweating manikin in an environmental chamber in accordance with Test Methods F1291, F2370, and F3426.