EPDM and nitrile are the two most commonly confused washer materials — and they're almost mirror opposites. Pick wrong and your washer can swell, crack or harden within weeks. Here's the clean decision.
The one-line answer
Oil or fuel? Choose nitrile. Outdoor water, weather or steam? Choose EPDM. They do not overlap well, so the medium decides it.
EPDM strengths and weaknesses
- Loves: sunlight, ozone, rain, steam, hot water, potable water
- Hates: petroleum oils, fuels and grease — these make it swell badly
- Temperature: -40°F to about 300°F
Nitrile (Buna-N) strengths and weaknesses
- Loves: motor oil, diesel, gasoline, hydraulic fluid, grease
- Hates: direct sunlight and ozone, which crack it over time
- Temperature: -40°F to about 250°F
Decision table
| If your washer will see… | Choose |
|---|---|
| Engine oil, fuel, hydraulics | Nitrile |
| Outdoor weather & UV | EPDM |
| Hot water or steam | EPDM |
| Both oil and sun | Viton |
Still deciding? The full material guide compares all seven compounds, and neoprene is a solid middle ground covered in our neoprene guide. When you're ready, shop by size here.