O-Ring Material: A Comparison of Materials
Four questions determine which O-ring material is suitable: What is the temperature at the installation site? What medium comes into contact with the ring? Does it move? And does it require approval? NBR is often sufficient for mineral oils; EPDM for water and steam; and FKM for high temperatures, oils, and chemicals. Where FKM reaches its limits, FFKM, FEP-coated O-rings, or PTFE provide a seal.
Operating temperature in air. Tap a material.
- The appropriate O-ring material depends on temperature, medium, motion, and certification. There is no single material that is best for all situations.
- NBR is the cost-effective standard for mineral oil and greases and is suitable for temperatures ranging from −30 °C to +120 °C. EPDM is the material of choice for water, steam, and brake fluid and is suitable for temperatures ranging from −45 °C to +150 °C.
- FKM is resistant to heat, oils, and chemicals from −25 °C to +200 °C; the special grade FKMEX40 ranges from −40 °C to +225 °C.
- FFKM is virtually universally resistant and, depending on the compound, can withstand temperatures up to +340 °C. At NH O-RING, it’s called ECOLAST.
- FEP-coated O-rings and PTFE are chemically resistant to virtually all substances. However, PTFE is not elastic.
Four Steps to Choosing the Right Material
The material selection process always follows the same sequence. Clarify these four points before comparing materials. After that, there are usually only one or two candidates left.
Record the lowest and highest temperatures at the installation site, including brief spikes. The values listed in the data sheet apply to air; in hot water and steam, the limits are often lower.
Check every fluid that comes into contact with the O-ring, including cleaning agents and assembly grease. Use the Fluid Compatibility Tool to evaluate individual fluids.
Static or dynamic—how high is the pressure, how wide is the gap? The material and hardness depend on these factors. Learn more under “O-Rings Under Pressure.”
The food, pharmaceutical, and hygiene industries require certifications such as FDA, USP Class VI, or 3-A. The composition is what matters, not the material name. For more information, see FDA Approval.
An Overview of the Most Important O-Ring Materials
NBR and EPDM are the traditional elastomers used for oil or water. The NH O-RING product line includes FKM, FFKM, FEP-coated O-rings, and PTFE. Each data sheet lists the operating temperature, hardness, and certifications, where applicable.
The affordable standard for mineral oil, fuel, and lubricants.
- Mineral Oil, Fuel, and Greases
- inexpensive standard material
- Ozone, weather, polar solvents
- Hot water up to 80 °C only; no steam
The material for water, steam, and glycol-based brake fluid.
- Hot water and steam up to 170 °C (peroxide-crosslinked)
- Glycol-based brake fluid
- Mineral oil and mineral oil-based greases
The most widely used high-performance material for heat, oils, and chemicals.
- Oils, fuels, and many chemicals
- Special Type FKMEX40: −40/+225 °C
- Hot water not recommended; steam up to 120 °C
Virtually universally resistant and elastic. Specifications for NH5750, high-temperature compounds up to +340 °C, and white grades for food and pharmaceutical applications.
- resistant to virtually all media
- Hot water and steam up to 270 °C (NH5755 HT)
- high price
Chemical-resistant outer layer, elastic core. Can be used at temperatures as low as −60 °C thanks to its silicone core.
- chemically resistant to almost all substances
- Hot water and steam up to 205 °C
- harder than elastomer O-rings (90 Shore A)
Chemically nearly inert, with the widest temperature range in this comparison.
- virtually inert, very low friction
- Not elastic; prone to cold flow
- only as a static flange gasket
Comparison of Temperature Ranges
The graph shows the operating temperature in air. Move the slider to your operating temperature: The materials whose temperature range includes this value will remain highlighted.
Operating temperatures in air according to NH material data, with NBR and EPDM for comparison. PTFE is suitable down to −250 °C; the scale starts at −100 °C. Temperature alone is not the deciding factor: Also check the medium, pressure, and certification.
Comparison Table: Temperature, Hot Water, Hardness, Certification
Materials behave differently in hot water and steam than they do in air. FKM can withstand temperatures of +200 °C in air, but is still not recommended for use in hot water. The table compares the two side by side.
| Material | Air | Hot water | Steam | Hardness | Approval | Storage |
|---|---|---|---|---|---|---|
| NBR for comparison | −30/+120 °C | up to 80 °C | Not recommended | depending on the mixture | depending on the mixture | N/A |
| EPDM (peroxide-cured), for comparison | −45/+150 °C | up to 170 °C | up to 170 °C | depending on the mixture | depending on the mixture | N/A |
| FKMFKM75S, FDA Type FKM75SFD | −25/+200 °C | Not recommended | up to 120 °C | 75 Shore A | FDA (FKM75SFD) | 10 years |
| FFKMECOLASTNH4700, white, food and pharmaceutical | −20/+270 °C | N/A | N/A | 70 Shore A | FDA, USP VI, 3-A | 15 years |
| FFKMECOLASTNH5750, Standard | −25/+270 °C | up to 210 °C | up to 210 °C | 75 Shore A | FDA | 15 years |
| FFKMECOLASTNH5751 HT, High Temperature | −15/+330 °C | up to 230 °C | up to 230 °C | 75 Shore A | EC 1935/2004 only | 15 years |
| FFKMECOLASTNH5755 HT, Steam and Hot Water | −15/+330 °C | up to 270 °C | up to 270 °C | 75 Shore A | EC 1935/2004 only | 15 years |
| FEP-coatedFEP-FKM | −25/+205 °C | up to 205 °C | up to 205 °C | 90 Shore A | FDA | 15 years |
| FEP-coated FEP-silicone | −60/+205 °C | up to 205 °C | up to 205 °C | 90 Shore A | FDA | 15 years |
| PTFEPTFE60, Solid Material | −250/+250 °C | up to 250 °C | up to 250 °C | 60 Shore D | FDA | virtually unlimited |
Air: Operating temperature as specified in the data sheet. Hot water and steam: Empirical values provided without warranty; if in doubt, test under actual operating conditions. Hardness is a nominal value; shelf life in accordance with DIN 7716 when stored properly. Regulation (EC) No. 1935/2004 applies to all NH compounds; the “Approval” column lists additional certifications. N/A: not available. All test results can be found in the data sheets.
NBR, EPDM, FKM, or FFKM? The Most Common Direct Comparisons
NBR or EPDM?
The choice depends on the medium. NBR is compatible with mineral oil, fuel, and greases; EPDM is compatible with water, steam, and glycol-based brake fluid. Conversely, EPDM is not resistant to mineral oil, and NBR can withstand hot water only up to 80 °C and cannot withstand steam at all. When oil and hot water come into contact, FFKM or FEP-coated O-rings are suitable options.
- Mineral Oil and Fats
- Fuel
- Steam
- Water and Steam
- Glycol-based brake fluid
- Mineral oil
FKM or NBR?
FKM is more durable: it withstands temperatures up to +200 °C instead of +120 °C and is resistant to a much wider range of chemicals. NBR, on the other hand, is less expensive and is sufficient for mineral oil and hydraulic oil at moderate temperatures. If the application is permanently outside the NBR range or if aggressive media are involved, FKM is usually the best choice.
- up to +200 °C
- Oils and many chemicals
- Hot water
- inexpensive
- Mineral oil and hydraulic oil
- above +120 °C
FKM or FFKM?
FFKM is fully fluorinated and therefore offers nearly universal resistance, whereas FKM reaches its limits with certain media. FFKM also has the edge when it comes to temperature: standard grades up to +270 °C, high-temperature grades up to +340 °C. The downside is the price, which is why FFKM is worth considering in applications where FKM is no longer sufficient. For more information, see the article on FFKM O-rings.
- up to +200 °C; special model up to +225 °C
- economically
- Gaps in some media
- virtually universally resistant
- up to +340 °C, depending on the mixture
- high price
FEP-coated or PTFE?
Both are chemically resistant to virtually all substances. The FEP-coated O-ring has an elastic core made of FKM or silicone, which provides restoring force. PTFE is a solid material with a temperature range from −250 °C to +250 °C, but it is not elastic and is therefore suitable only as a static flange gasket.
- elastic core
- FDA-compliant
- harder than elastomer O-rings
- −250/+250 °C
- virtually inert
- non-elastic
Approved Materials: Food, Pharmaceuticals, Oil, and Gas
In regulated industries, proof of the specific compound is essential. An FKM is not automatically FDA-compliant; the FDA-type FKM75SFD is. In the NH product line, these compounds have the following approvals:
Regulation (EC) No. 1935/2004 on materials intended to come into contact with food applies to all NH compounds. The white food- and pharmaceutical-grade types NH4700 and NH7700 use light-colored, food-grade fillers instead of carbon black. For more information, see FDA Approval and the glossary entries on USP Class VI, 3-A Sanitary, and NORSOK M-710.
Other elastomers and where they are used
In addition to the six main materials, there are materials designed for specific applications. You’ll find a separate article on each one in the Academy.
Common Mistakes in Material Selection
- EPDM assembled with mineral oil grease. EPDM is not resistant to mineral oil. Use silicone oil for installation; see the " O-Ring Installation" section for more information.
- FKM in hot water or steam. In air, FKM can withstand temperatures up to +200 °C; it is not recommended for use in hot water and can be used in steam only up to 120 °C. For water and steam, EPDM is generally the better choice.
- Only the steady-state temperature was tested. Cleaning, sterilization, and startup peaks often put more strain on the O-ring than normal operation.
- PTFE as an elastic substitute. PTFE is not elastic and is prone to cold flow. Where the ring needs to return to its original shape, FFKM or FEP-coated O-rings are suitable.
- More material than necessary. FFKM solves almost any media-related problem, but it is significantly more expensive. If FKM is sufficient, FKM is the more economical choice.
- Approval is based on the material name. Not every FKM is FDA-compliant. The key factor is verification of the blend.
Frequently Asked Questions About O-Ring Materials
Which O-ring material is the best?
Which O-ring material is heat-resistant?
Which material is suitable for hot water and steam?
Which O-ring materials are FDA-compliant?
Is FPM the same as FKM?
How do I determine whether a material is suitable for my medium?
How long can O-rings be stored?
Selection Tools
