The thermal resistance and evaporative resistance provided by a fabric, batting, or other type of material is of considerable importance in determining its suitability for use in fabricating protective clothing systems.

The thermal interchange between people and their environment is, however, an extremely complicated subject that involves many factors in addition to the steady-state resistance values of fabrics and battings. Therefore, thermal resistance values and evaporative resistance values measured on a hot plate may or may not indicate relative merit of a particular material or assembly for a given clothing application. While a possible indicator of clothing performance, measurements produced by the testing of fabrics has 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.

The thermal resistance of clothing systems can be measured with a heated manikin in an environmental chamber in accordance with Test Method F 1291.

Departures from the instructions of Test Method F 1868 may lead to significantly different test results. Technical knowledge concerning the theory of heat flow, temperature measurement, and testing practices is needed to evaluate which departures from the instructions are significant. Standardization of the method reduces, but does not eliminate the need for such technical knowledge. Report any departures from the instructions of Test Method F 1868 with the results.

1.1 This test method covers the measurement of the thermal resistance and the evaporative resistance under steady-state conditions, of fabrics, films, coatings, foams, and leathers, including multi-layer assemblies, for use in clothing systems.

1.2 The range of this measurement technique for thermal resistance is from 0.002 to 0.2 K-m2/W and for evaporative resistance is from 0.01 to 1.0 kPa-m2/W.

1.3 The values in SI units shall be regarded as standard.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.