Stem packing in API 6A manual and actuated valves uses live-loaded spring-energized PTFE or graphite-free hybrid designs. They achieve ISO 15848-1 fugitive emission Class BH and survive 200+ temperature cycles from -46°C to 200°C without leakage https://globalsealstech.com/product-category/oil-gas-seals/api-6a-wellhead-equipment-seals/