The function of insulating materials is to isolate the live parts with different potentials in electrical equipment. Therefore, electrical insulating materials should have high insulation resistance and withstand voltage strength, and can avoid leakage, breakdown and other accidents. In addition, it should also have good thermal conductivity, moisture resistance and lightning protection, high mechanical strength and convenient processing.

According to the above requirements, the performance indexes of allowable common electrical insulating materials include insulation strength, tensile strength, specific gravity, expansion coefficient, etc. Insulation withstand voltage strength: the higher the voltage applied at both ends of the insulator, the greater the electric field force on the charge in the material, and the easier ionization collision occurs, resulting in insulator breakdown. The low voltage that causes an insulator to break down is called the breakdown voltage of the insulator. When the 1 mm thick insulating material breaks down, the kilovolt voltage that needs to be added is called the insulation withstand voltage strength of the insulating material, which is called the insulation strength for short. As electrical insulating materials have a certain insulation strength, all kinds of electrical equipment, all kinds of safety appliances (Electrical pliers, electric pen, insulating gloves, insulating rods, etc.), all kinds of electrical materials, manufacturers have specified a certain allowable voltage, which is called rated voltage. When using, the voltage should not exceed its rated voltage value, so as to avoid accidents. Tensile strength: the tensile force that the insulating material can bear per unit cross-sectional area, for example, the glass can bear the tensile force of 1400 newton per square centimeter cross-sectional area. The insulation performance of electrical insulating materials is closely related to temperature. The higher the temperature, the worse the insulation performance of the insulating material. In order to ensure the insulation strength, each kind of insulation material has an appropriate allowable working temperature. Below this temperature, it can be used safely for a long time. If it exceeds this temperature, it will age rapidly. According to the degree of heat resistance, the insulating materials are divided into y, a, e, B, F, h, C and other grades.