coddy/iStock/Getty Images

When selecting a sealing washer, understanding the material’s chemical resistance, temperature range, and weather durability is crucial. Two of the most common synthetic rubbers—EPDM (ethylene propylene diene monomer) and nitrile (Buna‑N)—serve different needs. Below is a concise comparison to help you decide which is best for your system.

EPDM (Ethylene Propylene Diene Monomer)

EPDM is favored for water, steam, and automotive cooling lines, as well as brake systems. It excels in:

• Resisting mild acids, detergents, silicones, glycols, ketones, and alcohols
• Operating from –22 °F to 300 °F (–30 °C to 149 °C)
• Withstanding ozone and UV exposure when compounded for outdoor use

However, EPDM degrades in the presence of petroleum‑based fuels, oils, and solvents, making it unsuitable for fuel‑related sealing.

Nitrile (Buna‑N)

Nitrile is engineered from butadiene and acrylonitrile, offering superior protection against gasoline, diesel, motor oil, and other hydrocarbons. Key attributes include:

• Temperature tolerance from –65 °F to 275 °F (–54 °C to 135 °C)
• High resistance to petroleum products, ideal for automotive, marine, aviation, and stationary engine fuel systems
• Enhanced durability against weathering, ozone, and UV when formulated with additives

Its main limitation is susceptibility to sunlight and general weathering unless specifically compounded for outdoor use.

Use EPDM when you need a seal that handles high temperatures, mild chemicals, and water‑based environments. Choose nitrile for fuel systems or applications where oil resistance is paramount.