This part of BS 4745 specifies three methods for the determination of the resistance of fabrics, fabric assemblies or fibre aggregates in sheet form to the transmission of heat through them in the steady state condition. rt applies to materials whose thermal resistance is up to approximately 0.2 m²·K/W.

These methods are suitable for materials up to 20 mm thick (above this thickness, edge losses become appreciable). Advice on suitable components for constructing the apparatus is given in Annex A and means of calculating the thermal conductivity are described in Annex B.

Three methods are described:

Either of the two-plate methods is suitable for materials that, when in use, have their outer faces shielded from the ambient air, e.g a blanket when covered by a bedspread.

The single-plate method is suitable for materials that, when in use, have their outer faces exposed to the ambient air (e.g. bedspreads and outerwear).

The two-plate methods are generally preferred on accuracy and reproducibility grounds.