PEEK is a semicrystalline thermoplastic with excellent mechanical and chemical resistance properties that are retained to high temperatures. PEEK is used to fabricate items used in demanding applications, including bearings, piston parts, pumps, HPLC columns, compressor plate valves, and cable insulation. It is one of the few plastics compatible with ultra-high vacuum applications.

PEEK is second only in PI in special engineering plastics, but PEEK has better processability and wider processing window than PI to become a cost-effective engineering plastic. PEEK materials are often selected as the highest priority material between 120 and 260 °C.