Polymethyl methacrylate (PMMA) has less electrical properties than non-polar plastics such as polyolefin and polystyrene because of the presence of polar methyl group in the side of the main chain. The polarity of the methyl group is not very large, and PMMA still has good dielectric and electrical insulation properties. It is worth pointing out that PMMA and even the whole acrylic plastics have excellent arc resistance. Under the action of arc, there will be no carbonized conductive path and arc track on the surface. 20 ℃ is a second-order transition temperature, corresponding to the temperature at which the side methyl group begins to move. Below 20 ℃, the side methyl group is frozen, and the electrical properties of the material will be improved when the temperature is above 20 ℃.