This standard specifies a method for determining the thermal conductivity of refractory materials. The core principle involves applying a constant power to a pure platinum wire heater positioned between two test specimens. The rate of temperature increase of the heater wire depends on how quickly heat transfers to the constant-temperature portions of the specimens. By precisely measuring the change in the heater wire's resistance over time, the heating rate can be calculated. The thermal conductivity of the material is then derived using Fourier's law. This method is primarily applicable to refractory materials that are carbon-free, non-conductive, and have thermal conductivity not exceeding a specified limit. The test requires specialized equipment, typically involving the use of platinum resistance thermometers for accurate temperature measurement.