The function of insulating material is to isolate the charged parts with different potential in electrical equipment. Therefore, insulating materials should first have high insulation resistance and voltage strength, and can avoid leakage, breakdown and other accidents. Secondly, it has good heat resistance and avoids aging and deterioration due to long-term overheating. In addition, it should have good thermal conductivity, moisture and lightning resistance, high mechanical strength and easy processing. According to the above requirements, the performance indicators of common insulating materials are insulation strength, tensile strength, specific gravity, expansion coefficient and so on.

The common insulating materials used in electricians can be divided into inorganic insulating materials, organic insulating materials and mixed insulating materials according to their chemical properties. The commonly used inorganic insulating materials are mica, asbestos, marble, porcelain, glass, sulfur yellow, etc. They are mainly used for winding insulation of motors and electrical appliances, substrates and insulators of switches. Organic insulating materials include shellac, resin, rubber, cotton yarn, paper, hemp, rayon and so on. They are mostly used to make insulating paint and cover insulators for winding conductors. Mixed insulating materials are all kinds of moulding insulating materials made from the above two materials, which are used as base and shell of electrical appliances.