Anti-extrusion backup rings are mandatory in HPHT seals to prevent gap extrusion at 200+ MPa. PEEK, PTFE, and specially woven fabric/PEEK combinations are common. Spring-energized PTFE seals with metal springs provide near-zero leakage even after multiple RGD events, making them standard in subsea X-tree and downhole safety valves. https://globalsealstech.com/oil-gas-seals/