The original fluoroelastomer was a copolymer of hexafluoropropylene (HFP) and vinylidene fluoride (VF2). It was developed by the DuPont Company in 1957 in response to high performance sealing needs in the aerospace industry. To provide even greater thermal stability and solvent resistance, tetrafluoroethylene (TFE) containing fluoroelastomer terpolymers were introduced in 1959 and in the mid to late 1960’s lower viscosity versions of FKMs were introduced. A breakthrough in crosslinking occurred with the introduction of the bisphenol cure system in the 1970’s. This bisphenol cure system offered much improved heat and compression set resistance with better scorch safety and faster cure speed. In the late 70’s and early 80’s fluoroelastomers with improved low temperature flexibility were introduced by using perfluoromethylvinyl ether (PMVE) in place of HFP. These polymers require a peroxide cure. The latest FKM polymers have a much broader fluids resistance profile than standard fluoroelastomers, and are able to withstand strong bases and ketones as well as aromatic hydrocarbons, oils, acids, and steam.