The insulating material is used to isolate the charged part with different electric potential in the electrical equipment. Therefore, insulation materials should first have higher insulation resistance and compressive strength, and can avoid leakage, breakdown and other accidents. Secondly, heat resistance is better, avoid aging due to long-term overheating; in addition, it should also have good thermal conductivity, moisture resistance, lightning resistance and high mechanical strength, and convenient processing and other characteristics. According to the above requirements, the performance indexes of commonly used insulating materials include insulation strength, tensile strength, specific gravity, expansion coefficient, etc.

Insulating materials commonly used in electrical engineering can be classified into inorganic insulating materials, organic insulating materials and mixed insulating materials according to their chemical properties. The commonly used inorganic insulation materials: Mica, asbestos, marble, porcelain, glass, sulfur, mainly used for winding motor, electrical insulation, switch plate and insulator etc.. Organic insulating materials: shellac, resin, rubber, paper, cotton, linen, rayon, mostly used in the manufacture of insulating paint, winding insulation coating etc.. The mixed insulating material is made up of the two kinds of materials, and is used as the base and shell of the electric appliance.