Backup rings made from PTFE or PEEK are frequently combined with Norsok approved O-rings to prevent extrusion at pressures above 500 bar. Although the backup rings themselves are not rubber, the system qualification often includes the complete seal stack, proving that the Norsok approved elastomer works reliably with anti-extrusion devices in ultra-deepwater and HP/HT environments. https://globalsealstech.com/automotive/