In electrical equipment, the heat transfer characteristic of the medium has a great influence on the operating temperature and efficiency of the equipment. In some cases, the ability to conduct heat is a determinant factor to be considered when choosing an insulating medium. As a gas medium, its heat transfer characteristics mainly depend on its thermal conductivity, specific heat capacity and viscosity. Sulfur hexafluoride's excellent heat transfer properties determine its dominance as an insulating gas.

The classical heat conduction is to consider the thermal diffusion movement of gas molecules, so that the molecules in the high temperature region carry higher internal energy and migrate to the lower temperature region, resulting in the transfer of heat in space. By molecular motion I mean thermal motion, not macroscopic relative motion. As long as there is a temperature difference in space, there is conduction of heat.

In high temperature arc, sulfur hexafluoride will decompose and ionize, along with energy consumption, which has a great influence on the heat conduction process. Therefore, the thermal conductivity at this point can be considered to be composed of two parts, namely the standard thermal conductivity and the components related to decomposition and ionization reactions.

However, for gas medium, its heat transfer capacity is not only conduction, but depends on convective heat transfer to a large extent. The convective heat transfer is caused by the existence of local pressure difference, which causes the gas medium to produce macroscopic motion and diffuse the heat out. The convective heat transfer capacity of the gas medium is related to the specific heat capacity and viscosity of the gas.

Secondly, the diameter of sulfur hexafluoride molecules is larger than that of oxygen and nitrogen molecules in the air, so that the average free stroke of free electrons in sulfur hexafluoride gas is greatly shortened, so it is not easy to accumulate energy in the electric field, thus reducing the collision ionization capacity of free electrons.

In sulfur hexafluoride, the insulation strength of sulfur hexafluoride gas is very high because the net collision free coefficient of electricity is very small and the negative ion with low mobility is very easy to combine with the positive ion to form neutral molecules.

The insulation strength of sulfur hexafluoride gas remains basically unchanged in the range of frequency from power frequency to communication frequency at which ac voltage is applied externally. Therefore, sulfur hexafluoride gas is also widely used in many off-frequency electrical and electronic equipment, such as coaxial cable, waveguide, radar equipment and so on.