Thermal conductivity refers to the heat transferred through an area of 1 square meter in 1 second, in watts/meters · degrees W/(m·K), under stable heat transfer conditions, 1 meter thick material, the temperature difference on both sides of the surface is 1 degree (K, C).

The thermal conductivity is only for the heat transfer form with thermal conductivity. When there are other forms of heat transfer, such as radiation, convection, mass transfer and other forms of heat transfer, the composite heat transfer relationship. The composite heat transfer relationship is often referred to as the apparent thermal conductivity, the dominant thermal conductivity, or the effective thermal transmissivity of material. In addition, the thermal conductivity is for homogeneous materials, in the actual situation, there are also porous, multi-layer, multi-structure, anisotropic materials, the thermal conductivity obtained by this material is actually a comprehensive thermal conductivity performance, also known as the average thermal conductivity.

The thermal conductivity of different substances is different; The thermal conductivity of the same substance is related to its structure, density, humidity, temperature, pressure and other factors. The thermal conductivity of the material tends to increase with the increase of temperature or moisture content. Different from the influence caused by moisture, the increase of temperature will cause the acceleration of molecular thermal motion, promote the heat conduction of solid skeleton and the convective heat transfer of fluid in the pores.