O-Ring Chemical Compatibility
How to pick an O-Ring compound for your fluid: quick media rules, rating symbols, and a full chemical compatibility chart.
Picking a compound starts with one question: what will the seal touch? Media resistance is the first filter; temperature, pressure, and motion come next.
For the full searchable matrix (2,000+ fluids across twelve compounds, plus modern aliases like R-134a, biodiesel, and DEF), open the interactive Chemical Compatibility Chart (also under Compatibility in the nav)—based on the store Chemical Resistance Guide and expanded for HNBR, Butyl, PTFE, and current media.
How to read ratings
| Symbol | Meaning |
|---|---|
| ✓ | Suitable: no attack, or low attack |
| ~ | Limited: weak to moderate attack; test for your conditions |
| ✗ | Not recommended: severe attack to destruction |
| ※ | Special grade needed: the base polymer needs a specific formulation |
| ? | No reliable data, verify before use |
Ratings assume the stated test temperature and typical commercial concentration. Real service depends on concentration, temperature, pressure, exposure time, and the exact compound mixture—not only the polymer family.
Everyday media (quick view)
| Medium | Test °F | NBR | HNBR | FKM | FFKM | EPDM | VMQ | CR | AU |
|---|---|---|---|---|---|---|---|---|---|
| Mineral / hydraulic oil | 212 | ✓ | ✓ | ✓ | ✓ | ✗ | ~ | ✗ | ~ |
| Engine oil | 212 | ✓ | ✓ | ✓ | ✓ | ✗ | ~ | ~ | ~ |
| Diesel fuel | 140 | ✓ | ✓ | ✓ | ✓ | ✗ | ~ | ~ | ~ |
| Gasoline | 140 | ~ | ~ | ✓ | ✓ | ✗ | ✗ | ~ | ✗ |
| Water, hot | 212 | ✓ | ✓ | ~ | ~ | ✓ | ~ | ~ | ✗ |
| Steam | 266 | ✗ | ✗ | ※ | ✗ | ✓ | ✗ | ✗ | ✗ |
| Coolant / antifreeze (glycol) | 140 | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✗ |
| Brake fluid (glycol ether) | 176 | ✗ | ✗ | ? | ? | ✓ | ✓ | ~ | ? |
| Acetone (ketone) | 68 | ✗ | ✗ | ✗ | ✓ | ✓ | ✗ | ✗ | ✗ |
| Ethanol (alcohol) | 68 | ~ | ~ | ※ | ✓ | ✓ | ~ | ~ | ~ |
Need more chemicals (acids, bases, solvents, refrigerants, and specialty fluids)? Use the Chemical Compatibility Chart.
Patterns worth internalizing
- Petroleum (oils, fuels) → nitrile family and FKM; never EPDM.
- Water, steam, glycol brake fluid, ketones → EPDM; never nitrile for brake fluid.
- Aggressive chemicals + heat → FKM, and FFKM when nothing else survives.
- Polyurethane (AU) is a mechanical champion but chemically narrow—great in oil, poor in water, steam, acids, and bases.
See the Materials page for temperature ranges and the full character of each compound, or ask us with your fluid and temperature before ordering critical seals.
Charts are a rough guide only. Within a material class, different mixtures behave differently. For untested or critical service, verify against a full chart or test the actual compound.
Source: Freudenberg FST 2025 Technical Manual, ch. 2 §12 (Chemical Resistance), pp. 180–212. Ratings condensed to eight common O-Ring compounds.
