This part of ISO 8894 describes a hot-wire (parallel) method for the determination of the thermal conductivity of refractory products and materials. It is applicable to dense and insulating shaped products and to powdered or granular materials (see 6.2), for thermal conductivities of less than 25 W/m·K. The limits are imposed by the thermal diffusivity of the test material and therefore by the dimensions of the test pieces; higher termal conductivities can be measured if larger pieces are used. Electrically conducting materials cannot be measured. NOTE 1 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 can therefore require pretreatment. The nature and extent of such pretreatment, 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 2 In general, it is difficult to make measurements on anisotropic materials and the use of this method for such materials is also agreed between the parties concerned.