Fluoroelastomers (FKM) are one of the different types of rubber used as a packing material in shaft seals to prevent the pumped media from leaking.

The type of rubber used as packing material depends on the media and pressure in the system. Fluoroelastomer (FKM) covers a whole family of rubbers designed to withstand oil, fuel and a wide range of chemicals, including non-polar solvents. There are standard and special grades; the latter have special properties, such as improved resistance to low temperature operation and chemicals.

FKMs offer excellent resistance to high temperature operation in different types of oil (up to 200°C depending on the grade of FKM). Fluoroelastomer rubbers have limited resistance to steam, hot water, methanol and other highly polar fluids. This type of rubber has poor resistance to amines, strong alkalis and many freons.