Thermal conductivity is the amount of heat passing through a unit area per unit time when the temperature drop in the object is 1 ° C. Its unit is W / m · k. The numerical value of the thermal conductivity expresses the magnitude of the material's thermal conductivity. The thermal conductivity values of various materials used in engineering calculations are generally determined by experiments. Thermal conductivity is generally related to the density, temperature, humidity and heat flow direction of the material.