This Technical Specification specifies the conditions for the determination of the thermal diffusivity of single filaments of ceramic fibres parallel to the fibre axis. This Technical Specification applies to continuous ceramic filaments taken from tows, yarns, braids and knittings. The experimental conditions are such that the material behaves in an homogeneous manner and that the heat transfer occurs only by thermal conduction. The method is applicable to materials which are physically and chemically stable during the measurement, and covers the range of temperature between 100 K and 600 K. It is suitable for the measurement of thermal diffusivity values in the range between 10-4 m²Î*s-1 and 10-7 m2Î*s-1.