The main foreign production is polyethylene (PE), while the main domestic production is polypropylene (PP), which is a thermoplastic resin made by polymerizing ethylene. In industry, it also includes copolymers of ethylene with small amounts of alpha olefins. Polyethylene is odorless, non-toxic, and feels like wax. It has excellent low temperature resistance (up to -70~-100 ℃ for low use), good chemical stability, and can withstand most acid and alkali corrosion (not resistant to oxidizing acids). It is insoluble in general solvents at room temperature, has low water absorption, and excellent electrical insulation performance; But polyethylene is very sensitive to environmental stress (chemical and mechanical effects) and has poor heat aging resistance. The properties of polyethylene vary depending on the variety, mainly determined by its molecular structure and density. By using different production methods, products with different densities (0.91-0.96g/cm3) can be obtained.