Hybrid packing combining PCTFE primary seals with PTFE/graphite intermediates offers the best compromise of low permeation and fire safety. This configuration achieves both cryogenic performance and post-fire resealing capability in a single stack for critical LNG isolation valves. https://globalsealstech.com/product-category/oil-gas-seals/api-6d-ball-valve-and-lng-seals/