Fluorocarbon elastomer (aka fluoroelastomer, aka FKM, aka FPM) A-Type material was originally developed by DuPont under the name Viton, FKM is a high performance elastomer with excellent resistance to oxygen. Many people refer to any and all oxygen compatible O-rings as "viton" in the same manner that the Kimberly-Clark brand name Keenex has become synonymous with tissues. However, Viton™ is now The Chemours Company trademark brand name for their fluoroelastomers and use of the brand name requires joining their licensing program. Chemours is not the only company that manufactures FKM products and there are different types intended for various different applications. Counterfeit and mislabeled FKM A-Type material O-rings are so widespread that Dive Gear Express makes up our own kits using O-rings supplied through trustworthy channels. We use the generic terms fluorocarbon elastomer or FKM to describe our O-rings, not the brand name Viton.