This part of ISO 8894 describes the hot-wire methods (“cross-array” and “resistance thermometer”) for the determination of the thermal conductivity of non-carbonaceous, dielectric refractory products and materials. This methods are applicable to dense and insulating refractories (shaped products, refractory castables, plastic refractories, ramming mixes, powdered or granular materials) with thermal conductivity values less than 1,5 W/m·K (“cross-array”) and less than 15 W/m·K (“resistance thermometer”) and thermal diffusivity values less than 5 × 10-6 m2/s. Thermal conductivity values can be determined at a room temperature up to 1 250 °C. The maximum temperature (1 250 °C) can be reduced by the maximum service limit temperature of the refractory, or by the temperature at which the refractory is no longer dielectric. NOTE 1 In general, it is difficult to make accurate measurements on anisotropic materials and the use of this method for such materials can be agreed between the parties concerned. NOTE 2 The thermal conductivity of products with a hydraulic or chemical bond can be affected by the appreciable amount of water that is retained after hardening or setting and is released on firing. These materials might therefore require pre-treatment; the nature and extent of such pre-treatment and the period for which the test piece is held at the measurement temperature as a preliminary to carrying out the test, are details that are outside the scope of this part of ISO 8894 and are agreed between the parties concerned. NOTE 3 The measurement of thermal conductivity is not sufficiently uncomplicated for an engineer to expect to achieve correct results without having particular work experience and if the work is based exclusively on this standard. Sufficient experience of measuring temperatures and laboratory skills are imperative.