PEEK (polyetheretherketone) is the primary anti-extrusion material in API 6A seals. Virgin and carbon-filled grades resist 260°C continuously, show near-zero swell in H2S/CO2, and prevent elastomer extrusion at 25,000 psi in tubing hangers and gate valves. https://globalsealstech.com/product-category/oil-gas-seals/api-6a-wellhead-equipment-seals/