According to structures of polymer materials, thermoplastic plastics are divided into non-crystallite plastic and semi-crystallite plastic. Non-crystallite plastic is usually transparent, but stress cracking often appears during use and processing. Due to high dimensional stability, it is suitable for manufacturing precision components. Semi-crystallite plastic is non-transparent, most of which has good stiffness and excellent chemical resistance. Plastics are classified according to their heat resistance property. High temperature plastic:its long-term operating temperature is over 150℃, which has excellenttemperature-mechanical properties. Some plastics are suitable to use for high temperature (e.g. PI, PBI and PTFE) can not be processed by welding but sintering. Engineering plastic: plastic suitable to use for long-term use at a temperature ranging from 100 to 150℃, has good mechanical property and chemical resistance. General plastic: plastic suitable to use for long-term use at 100℃ or less. Classification in accordance these standards are detailed illustrated in the above plastic pyramid.