Another of the high performance, high temperature resistant polymers, possessing very good physical and electrical insulation properties, PEI, like many of the other SPECIALTIES has applications in such high-tech areas as aerospace, aircraft, medical and electronics. As well, PEI has good chemical resistance, for an amorphous polymer, and has excellent flame resistance with low smoke generation when exposed to flames. Due to the ease of processing, the cost of the enhanced benefits of PEI over other engineering polymers such as Nylons, PET and Acetals is not as dramatic as with many of the other SPECIALTIES. PEI retains much of its high modulii at higher temperatures while maintaining stable electrical insulation characteristics over wide thermal and frequency ranges. In addition, PEI can be repeatedly autoclaved without degradation. And PEI has very good resistance to gamma and UV radiation. PEI is attacked by common organic solvents thus water or water-soluble oils can only be used for machining. With high stiffness, hardness, temperature resistance and low coefficient of thermal expansion, PEI has very good machinability. High speed tooling run at high speeds and high feeds produces very good finish and high tolerance parts. Carbide should be used with glass filled grades. PEI suffers from poor notch impact resistance and this must be considered and compensated for in any part design. With its susceptibility to organic solvents, PEI responds well to solvent cementing. As with other high temperature resistant polymers, hot gas welding, spin welding and butt-welding procedures can be successful if sufficient heat can be put into the weld area.