O-ring selection is based on chemical compatibility, application temperature, sealing pressure, lubrication requirements, durometer, size and cost.
Synthetic rubbers - Thermosets:
Butyl rubber (IIR)
Epichlorohydrin rubber(ECH, ECO)
Ethylene propylene diene monomer (EPDM): good resistance to hot water and steam, detergents, caustic potash solutions, sodium hydroxide solutions, silicone oils and greases, many polar solvents and many diluted acids and chemicals. Special formulations are excellent for use with glycol-based brake fluids. Unsuitable for use with mineral oil products: lubricants, oils, or fuels. Peroxide-cured compounds are suitable for higher temperatures.
Fluoroelastomer (FKM): noted for their very high resistance to heat and a wide variety of chemicals. Other key benefits include excellent resistance to aging and ozone, very low gas permeability and the fact that the materials are self-extinguishing.
Polychloroprene (neoprene) (CR)
Silicone rubber (SiR): noted for their ability to be used over a wide temperature range and for excellent resistance to ozone, weathering and aging. Compared with most other sealing elastomers, the physical properties of silicones are poor. Generally, silicone materials are physiologically harmless so they are commonly used by the food and drug industries. Standard silicones are resistant to water (to 100 °C), aliphatic engine and transmission oils and animal and plant oils and fats.
Styrene butadiene rubber (SBR)