This is a thermopolymer of hexafluoropropylene and polyvinyldene, commonly known as FKM.

Viton® has been proven to have better fluid-resistant properties than other commercial rubbers. It has excellent resistance to oils, fuels, lubricants, most mineral acids and many aliphatic and aromatic hydrocarbons, such as carbon tetrachloride, toluene and xylene. On the other hand, its use is not recommended with ethers and low-molecular-weight ethers, ketones, amine ribbons, hydrofluoric acid and hot anhydrous chemicals, or chlorosulphonic acid.