Tetrafluoroethylene propylene (FEPM, commonly known as Aflas) fills the gap between FKM and evolast® FFKM, and it is specified primarily for chemical environments that attack fluorocarbon. It offers excellent resistance to amines, caustics, steam, hot water, sour gas, and the corrosion inhibitors and completion fluids used in oil and gas production, with continuous service to roughly 450°F (232°C). Moss Seal supplies FEPM for downhole and wellhead service where H2S, high pH, and hot water are present together. The trade-offs are poor low-temperature flexibility, typically limited to around 30°F (-1°C), and reduced resistance to some hydrocarbons compared with FKM, so the compound is selected against the specific fluid rather than as a general upgrade.