Coated O-rings, also called "fluorine-coated O-rings" and "silicon-coated O-rings", etc., using FEP or PFA special high temperature resistant fluoroplastics on the outside, and elastic rubber (fluorine/silicone, etc.) Q-rings on the inside It is compounded by a special process. Ordinary rubber O-rings are easy to wear, chemically resistant, and poorly resistant to gas penetration. Pure PTFE tetrafluoro O-rings have higher hardness and can resist compression but have poor elasticity. The O-ring covered with FEP or PFA has good resistance to swelling and chemical stability (unless it is attacked by alkali metals, fluorine and some halides at high temperatures). It has good elasticity near the rubber O-ring The friction coefficient of FEP or PFA is very small (only 0.08~0.2), and has excellent gas permeability resistance, these properties make the coated O-ring can be truly used in harsh environments.