This standard specifies the heat flow meter method for determining the thermal conductivity of insulating materials in the form of sheets or blankets, granular material being generalizable. NOTE- Given that in a large part of thermal insulating materials (cellular plastics), an important part of the heat transferred is due to the phenomenon of radiation through its structure, the results of this technique give values of thermal conductivity, which They are not independent of the thickness of the tested sample. The method, which is, compared to others, relatively fast, is based on a prior calibration of the apparatus, which must be carried out using samples measured with a heating plate type apparatus with guard ring and double cooling plate (see standard UNE 92-201). Two types of provisions can be used, the use of which gives satisfactory results in both cases. a) Symmetrical arrangement, shown in Figure 1 (method S), in which case the heat flow meter is placed in a central position between two identical test samples. b) Asymmetrical arrangement, shown in Figure 2 (AS method), in which case the heat flow meter is placed next to a single test sample.