Polyetheretherketone (PEEK) is a high-performance semi-crystalline thermoplastic used where a polymer has to carry real mechanical load at temperature. It offers continuous service to roughly 480°F (250°C), excellent strength and creep resistance, low wear, good radiation resistance, and broad chemical compatibility, with the notable exception of concentrated sulphuric acid. Moss Seal machines PEEK in virgin, glass-filled, carbon-filled, and bearing-grade compounds. It is the standard choice for back-up rings in high-pressure and high-temperature service, anti-extrusion devices, valve seats, bearings, wear rings, and downhole components where PTFE would cold flow and metal would be too heavy or too aggressive on mating surfaces.