low temperature insulation materials can be divided into polymer materials, composite materials and ceramic materials according to their types. For the application of superconducting power devices, low temperature insulation materials are mainly used in the form of thin films, adhesives and structural materials.

In order to reduce the insulation duty, it is necessary to use thin film insulation materials with good mechanical properties. The higher tensile fracture strength can also reduce the thickness of the film and the number of layers, thus further reducing the duty of the insulation part. As mentioned in the previous chapter, the commonly used superconducting industrial insulation films are: polyimide film (PI), polytetrafluoroethylene film (PTFE), polypropylene film (PP), polyester film (PET), polynaphthalene ester film (PEN), polyethylene film (PE), etc. Because of its excellent mechanical properties, high and low temperature resistance, high electrical breakdown strength and good chemical stability, PI thin film is the most ideal low temperature insulating film material at present.

In polymer insulating films, PI and PTTEE films have been widely used in superconducting, cryogenic engineering and cryogenic physics experiments due to their excellent electrical and chemical stability at low temperatures. PTFE thin films can work in the range of - 250 - 250 C, with low dielectric loss, little change in the wide temperature band and no carbonization under the action of arc. At high temperature, the tensile strength decreases, the elongation increases, and at low temperature, the tensile strength increases, and the elongation decreases. However, the obvious disadvantage of PTFE film is its low mechanical properties and anisotropy, and it is not easy to bond at low temperature. In addition to most of the advantages of PTFE films, PI films can maintain softness at liquid nitrogen and helium temperatures, resist almost all organic solvents and acids, and have good wear resistance, arc resistance and high energy irradiation resistance. PI films irradiated by gamma rays at 1010 erg/g still maintain good tensile strength and elongation. PI film has the characteristics of strong designability, easy processing and modification. These characteristics make PI thin films the most widely used thin films in superconducting insulating materials, especially in high temperature superconductors around 77 K and low temperature superconductors at 4.2 K.