Materials
O-Ring Material Selection — Temperature, Media and Physical Properties
Continuous temperature ranges, media compatibility and typical physical properties for NBR, HNBR, FKM, EPDM, silicone, polyurethane and FFKM O-ring compounds, plus hardness and approvals guidance.
- Reading
- 9 min
- Updated
- 2026-08-08
- Published
- 2026-08-08
- Category
- Materials
Material selection is two questions asked in order: will the compound survive the temperature, and will it survive the medium? Get either wrong and no amount of groove design will save the joint. This page is the working comparison we use at the enquiry desk.
The elastomer families
| Family | Code | Typical range (°C) | Short excursion | Character |
|---|---|---|---|---|
| Nitrile | NBR | −30 to +100 | +120 | The default. Best all-round balance of oil resistance, strength and cost |
| Low-temperature nitrile | NBR (LT) | −48 to +80 | +100 | Cold-start duty; trades heat resistance for flexibility |
| Hydrogenated nitrile | HNBR | −30 to +150 | +165 | Nitrile chemistry with far better heat, ozone and wear resistance |
| Fluoroelastomer | FKM | −20 to +200 | +220 | Heat, fuels, most oils and many chemicals; poor in hot water, steam, brake fluid, ketones |
| Ethylene propylene | EPDM | −45 to +130 | +150 | Water, steam, glycol coolant, brake fluid, ozone. Never with mineral oil |
| Silicone | VMQ | −60 to +200 | +230 | Extreme temperature range, food/medical; weak, poor abrasion and fluid resistance |
| Fluorosilicone | FVMQ | −60 to +175 | +200 | Fuel resistance plus low-temperature flexibility. Static duty only |
| Polyacrylate | ACM | −20 to +150 | +165 | Hot engine and transmission oils with additive packages |
| Perfluoroelastomer | FFKM | −15 to +300 | +325 | Near-universal chemical resistance at high temperature; premium cost |
| Polyurethane | AU/EU | −30 to +80 | +100 | Very high strength, extrusion and abrasion resistance. Hydrolyses in hot water |
Media compatibility
The table below is a first-pass screen. ✓ = suitable, ~ = conditional (check the specific fluid, additive package and temperature), ✗ = do not use.
| Medium | NBR | HNBR | FKM | EPDM | VMQ | FFKM |
|---|---|---|---|---|---|---|
| Mineral hydraulic oil | ✓ | ✓ | ✓ | ✗ | ~ | ✓ |
| Engine / gear oil | ✓ | ✓ | ✓ | ✗ | ~ | ✓ |
| Petrol / gasoline | ~ | ~ | ✓ | ✗ | ✗ | ✓ |
| Diesel | ✓ | ✓ | ✓ | ✗ | ✗ | ✓ |
| LPG / natural gas | ✓ | ✓ | ✓ | ✗ | ✗ | ✓ |
| Water to 80 °C | ✓ | ✓ | ~ | ✓ | ~ | ✓ |
| Hot water / steam | ✗ | ~ | ✗ | ✓ | ✗ | ✓ |
| Glycol coolant (LLC) | ~ | ✓ | ~ | ✓ | ~ | ✓ |
| Glycol brake fluid (DOT 3/4) | ✗ | ✗ | ✗ | ✓ | ✗ | ✓ |
| HFC / water-glycol fluids | ✓ | ✓ | ~ | ✓ | ~ | ✓ |
| Phosphate ester (HFD-R) | ✗ | ✗ | ~ | ✓ | ~ | ✓ |
| Dilute acids | ~ | ~ | ✓ | ✓ | ~ | ✓ |
| Dilute alkalis | ~ | ~ | ~ | ✓ | ~ | ✓ |
| Ketones (acetone, MEK) | ✗ | ✗ | ✗ | ✓ | ✗ | ✓ |
| Alcohols | ~ | ~ | ~ | ✓ | ✓ | ✓ |
| Aromatics (benzene, toluene) | ✗ | ✗ | ✓ | ✗ | ✗ | ✓ |
| Ozone / weathering | ✗ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Compressed air, dry | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
| Silicone oil / grease | ✓ | ✓ | ✓ | ✓ | ✗ | ✓ |
Hardness and its consequences
| Shore A | Extrusion resistance | Conformability | Typical duty |
|---|---|---|---|
| 60 | Low | Excellent | Low pressure, rough faces, cold service |
| 70 | Moderate | Good | General hydraulic and static — the default |
| 80 | Good | Moderate | Higher pressure, larger clearance |
| 90 | High | Poor | High pressure, usually with a back-up ring |
Typical physical properties
Representative values for well-formulated 70 Shore A compounds. Use these to sense-check a quoted specification, not as a purchase specification in themselves.
Mechanical properties
| Property | NBR | HNBR | FKM | EPDM | VMQ |
|---|---|---|---|---|---|
| Hardness (durometer A) | 70 ± 5 | 70 ± 5 | 70 ± 5 | 70 ± 5 | 70 ± 5 |
| Tensile strength (MPa) | 15–20 | 20–28 | 10–14 | 12–19 | 6–9 |
| Elongation at break (%) | 220–300 | 250–350 | 150–200 | 200–280 | 180–280 |
| Modulus at 100 % elongation (MPa) | 5–7 | 6–9 | 4–6 | 4–6 | 2–4 |
| Compression set, 70 h (%) | 8–15 at 100 °C | 10–20 at 150 °C | 10–25 at 200 °C | 5–15 at 120 °C | 15–30 at 200 °C |
| TR10 low-temperature value (°C) | −25 to −50 | −25 | −18 | −45 to −50 | −60 |
TR10 (temperature-retraction at 10 % recovery from 50 % elongation) is the most useful single indicator of low-temperature capability. It marks the point at which the compound recovers only 10 % of an imposed deformation — in practice, the temperature at which the ring stops behaving like a spring and starts behaving like a plastic. Treat TR10 as the realistic low-temperature limit for a static seal and add margin for dynamic duty.
Ageing and fluid resistance
| Test | Condition | Acceptable change | Why it matters |
|---|---|---|---|
| Heat ageing | 70 h at rated temperature | Hardness +10 pts, tensile −15 %, elongation −40 % | Predicts long-term embrittlement |
| Compression set | 70 h at rated temperature | Under 25 % (static), under 20 % (dynamic) | The single best predictor of seal life |
| Fluid immersion | 70 h in the service medium | Volume change −5 % to +10 % | Swell over-fills the groove; shrinkage loses squeeze |
| Hardness change in fluid | 70 h in the service medium | ±5 points | Large drops indicate plasticiser extraction |
| Low temperature | TR10 | At or below the coldest service temperature | Below TR10 the ring cannot recover |
A note on colour coding
Colour is a convenience, not a specification. Black covers nitrile, HNBR, EPDM and most FKM; brown and green FKM, violet and blue EPDM and FKM variants, and white or blue for food-contact and detectable compounds are all in common use, but conventions differ between manufacturers. Always specify by material, hardness and compound reference — never by colour alone.
Approvals and regulated service
Potable water, gas, food and pharmaceutical applications need an approved compound, not simply a compatible one. Typical schemes are WRAS and KTW for potable water, EN 549 and BS EN 682 for gas, FDA 21 CFR 177.2600 and EC 1935/2004 for food contact, and USP Class VI or 3-A for pharmaceutical and dairy duty. Compound approval is granted to a specific formulation, so a "WRAS-approved EPDM 70" is a named compound, not a generic material — always order by the approved compound reference and keep the certificate with the job.
Frequently asked questions
- What temperature can a nitrile O-ring take?
- A general-purpose NBR runs continuously from about −30 °C to +100 °C, with short excursions to +120 °C. Low-temperature nitriles reach −48 °C but give up heat resistance; HNBR extends the upper limit to about +150 °C.
- Is FKM always better than nitrile?
- No. FKM handles heat, fuels and aromatics far better, but it is attacked by hot water, steam, glycol brake fluid, ketones and amines — all applications where EPDM performs better and costs less.
- Which O-ring material should I use with water and steam?
- EPDM. It handles hot water, steam, glycol coolants and brake fluid, and resists ozone. Never use EPDM with mineral oil, which swells it uncontrollably.
- What is TR10 and why does it matter?
- TR10 is the temperature at which a compound recovers only 10 % of an imposed deformation. It is the most reliable indicator of the practical low-temperature limit of an O-ring — below TR10 the rubber no longer behaves elastically.
- Can I identify an O-ring material by its colour?
- Not reliably. Colour conventions differ between manufacturers and black covers most families. Specify by material, hardness and compound reference.
Related articles
- Technical ArticlesHow an O-Ring Actually Seals — Squeeze, Reaction Force and Pressure EnergisingThe mechanics behind O-ring sealing: installed squeeze, reaction force, pressure energising, groove fill, hardness against extrusion, surface finish targets and compression set.
- Technical ArticlesO-Ring Groove Design — Squeeze, Fill, Elongation and Back-Up RingsWorking reference for O-ring groove design: piston, rod, flat-face and dovetail configurations, squeeze and groove fill targets, elongation limits, three-sided grooves and back-up ring selection.
- Engineering Q&AO-Ring Storage, Shelf Life and HandlingHow long O-rings last in storage by material, correct storage conditions, why rings must never be hung or stretched, what white blooming means, and safe handling at the point of fitting.
- MaterialsSakagami Materials — Physical Properties ReferencePhysical properties of Sakagami NBR, HNBR, NBR blends, EPDM, FKM, S-KID and polyurethane compounds: hardness, tensile strength, elongation, temperature range and TR10 low-temperature data.
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