Thermal conductivity of insulations using guarded hot plates, including recent developments and sources of reference materials

The hot plate technique for measuring the thermal conductivities (the exact term for the quantity measured is thermal transmission, which, depending on the material being measured, can have components of convective, radiative and conductive heat transfer; it is commonly referred to as the effective or apparent thermal conductivity) of insulating materials has been in existence in various forms since 1898. A brief historical survey of the early development of the experimental technique is followed by a brief description of the basic principles of the method of measurement. The technique has since become very well established and is documented in the written standard ISO8302:1991. It is now unarguably recognized as the most accurate technique for determining the thermal conductivity of insulations, having an uncertainty of about 1.5% over a limited temperature range near ambient.