Viton® is a synthetic rubber and fluoropolymer elastomer commanly used in o-rings. It is a trademarked name of the DuPont corporation.

Most Viton ® elastomers are categorized under the ASTM D1418 designation of FKM. This class of elastomer is further categorized by types. Type-1 FKM: is a copolymer of hexafluoropropylene (HFP) and vinylidene fluoride (VDF or VF2). A Type-1 Viton is generally 66% fluorine by content. Type-2 FKM: is a terpolymer of tetrafluoroethylene (TFE), vinylidene fluoride (VDF), and hexafluoropropylene (HFP). A Type-2 Viton is generally 68% fluorine by content.