Silicone waterproof sealing ring is used to isolate different conductive solids. Solid insulating materials are also required to be supportive. Solid insulation material due to high density, so the breakdown strength is much higher, solid insulation material insulation resistance, dielectric constant and the range of change is very wide.

Solid insulating materials can be divided into two categories, inorganic and organic.

Inorganic solid insulation materials: mainly powder mica and mica products, glass, glass fiber and its products, as well as porcelain, alumina film. They are resistant to high temperature, not easy to aging, with considerable mechanical strength, some of the materials such as, low cost, occupy a certain position in the application.

Glass is simpler than ceramic and can be made. Glass fiber can be made into silk, cloth, tape, with much higher heat resistance than organic fiber, in the insulation structure to high temperature development plays an important role.

Organic solid insulation materials: in the 19th century to the main natural, such as paper, cotton, silk, can be cured vegetable oil. These materials are flexible, can meet the application process requirements, and easy to obtain.

Silicone resin combined with less alkali glass cloth, greatly improve the heat resistance grade. The enameled wire that polyethylene suo formaldehyde makes for enameled base opened up the broad prospect of enameled wire, replaced filar wire and gauze wire. The thickness of polyester film is only dozens of microns, and it can replace the original paper and cloth, so that the technical and economic indicators of motor and electrical appliances are greatly improved. Polyaromatic amide fiber paper, polyester film and polyimide film are used together to make the heat resistance grade of motor tank insulation F and H respectively. Similar developments have taken place in elastomer materials, such as heat resistant silicone rubber, oil resistant nitrile rubber, and later fluororubber, ethylene propylene rubber, etc.