NBR vs FKM vs EPDM O-Rings
Jul 22, 2026
Choose by media first, then check temperature and service life.
Use NBR for most mineral-oil systems running at moderate temperatures. Move to FKM when heat, fuel exposure or hydrocarbon resistance pushes NBR beyond a reliable working range. Use EPDM for water, glycol, ozone and outdoor service when petroleum oil is absent. A more expensive material only saves money when it corrects the actual failure mechanism.
Quick Material Comparison
| Selection Factor | NBR | FKM | EPDM |
|---|---|---|---|
| Best starting point | Mineral hydraulic oil, lubricating oil, grease and general industrial equipment. | Higher-temperature oil, fuel, aromatic hydrocarbons and many chemical duties. | Water, glycol coolant, outdoor equipment, ozone exposure and selected steam service. |
| Typical screening range | About -30 to 100°C Special compounds may extend higher. |
About -20 to 200°C Low-temperature and high-temperature grades vary. |
About -40 to 150°C Steam performance depends heavily on the compound. |
| Mineral oil resistance | Very good for most common grades. | Excellent, especially at higher temperature. | Poor. Mineral oil usually causes swelling and softening. |
| Water resistance | Acceptable in many moderate-temperature water applications. | Compound-dependent. Standard FKM needs careful review in hot water and steam. | Very good for water, glycol and suitable steam systems. |
| Ozone and weather | Limited. Cracking can develop during prolonged outdoor exposure. | Excellent ozone and weather resistance. | Excellent ozone, UV and outdoor resistance. |
| Relative material cost | Low | High | Low to moderate |
| Main reason for rejection | High heat, ozone, outdoor exposure or incompatible polar solvents. | Ketones, amines, selected esters and ethers, or unsuitable hot-water and steam service. | Petroleum oil, hydrocarbon fuel and oil-based lubricants. |
Temperature values are screening ranges. Polymer type, cure system, hardness, fluid exposure, pressure, motion and test duration can change the usable limits. Approve the compound specification rather than buying from the material name alone.
NBR O-Rings: The Practical Choice for Oil Service
NBR O-rings, also called nitrile or Buna-N O-rings, cover a large share of hydraulic, pump, valve and general machinery requirements. NBR offers a useful balance of oil resistance, abrasion resistance, molding stability and price.
Select NBR when the application includes:
- Mineral-based hydraulic oil at moderate temperature.
- Lubricating oil, grease or general petroleum-based fluids.
- Reciprocating hydraulic or pneumatic equipment with suitable lubrication.
- Cost-sensitive replacement parts with predictable maintenance intervals.
- Pumps, valves, gearboxes and industrial machinery installed indoors.
NBR begins to lose its cost advantage when it is held near its upper temperature limit for long periods. The seal may harden, flatten and stop recovering after shutdown. Leakage often appears during the next cold start rather than while the equipment is hot.
Avoid standard NBR in long-term outdoor exposure, high-ozone environments, ketones, many esters, strong oxidizing media and continuous high-temperature service. Increasing hardness may reduce extrusion, but it will not correct chemical attack or heat aging.
FKM O-Rings: Higher Heat and Hydrocarbon Resistance
FKM O-rings are commonly selected for hot oil, automotive fuel systems, industrial pumps and valves, and equipment exposed to aromatic or hydrocarbon-based media. They also resist ozone and outdoor aging much better than standard NBR.
Upgrade from NBR to FKM when:
- Continuous oil temperature repeatedly hardens or flattens NBR.
- Fuel, aromatic hydrocarbons or aggressive oil additives cause excessive NBR swelling.
- The seal is exposed to both petroleum media and outdoor ozone.
- Longer maintenance intervals justify the higher material cost.
- Downtime costs more than the difference between an NBR and FKM seal.
FKM is frequently ordered as a universal premium material. That approach creates expensive failures when the actual media is incompatible. Standard FKM compounds can perform poorly in ketones, hot amines, some low-molecular-weight esters and ethers, and certain hot-water or steam conditions.
Provide the full chemical name instead of writing "chemical liquid" on the RFQ. Different FKM polymer and cure systems can produce noticeably different results in fuels, acids, bases and steam.
EPDM O-Rings: Water, Glycol and Outdoor Exposure
EPDM O-rings are widely used in water equipment, coolant systems, outdoor valves and applications exposed to ozone or weather. Suitable peroxide-cured compounds can also provide reliable performance in hot water and selected steam duties.
Select EPDM when the application includes:
- Cold or hot water without petroleum contamination.
- Water-glycol coolant and many glycol-based fluids.
- Outdoor pumps, valves, fittings and exposed equipment.
- Ozone, UV, rain and long-term weather exposure.
- Selected dilute acids, alkalis and polar media after compatibility review.
Mineral oil is the quickest reason to reject EPDM. Even a water system can become unsuitable when oil-based assembly grease, compressor oil or process contamination reaches the seal. Swelling may begin slowly and then accelerate as the softened O-ring moves toward the extrusion gap.
For potable water, food equipment or regulated applications, specify the exact approval needed. A black EPDM O-ring and a WRAS-, NSF- or food-contact-compliant EPDM compound should not be treated as interchangeable products.
Oil, Water, Ozone and Heat Comparison
| Operating Condition | First Material to Review | Why | Main Check Before Approval |
|---|---|---|---|
| Mineral hydraulic oil below about 100°C | NBR | Good oil resistance and economical replacement cost. | Oil additives, peak temperature, pressure gap and dynamic wear. |
| Hot hydraulic or lubricating oil | FKM | Better heat aging and seal-force retention at elevated temperature. | Low-temperature startup, fluid additives and decompression conditions. |
| Gasoline, diesel or hydrocarbon fuel | FKM | Strong resistance to many fuels and aromatic hydrocarbons. | Fuel blend, alcohol content, temperature and permeation requirements. |
| Cold water or water-glycol coolant | EPDM | Good water, glycol and weather resistance. | Oil contamination, corrosion inhibitors and compliance requirements. |
| Hot water or steam cleaning | Verified EPDM compound | Suitable peroxide-cured EPDM grades can retain sealing force in hot-water service. | Steam temperature, pressure, cycle time, cleaner and sanitation chemicals. |
| Outdoor water valve | EPDM | Strong ozone, UV, water and weather resistance. | Petroleum grease used during installation and actual water chemistry. |
| Outdoor equipment containing petroleum oil | FKM or application-specific NBR | EPDM is excluded by the oil. FKM provides both oil and ozone resistance. | Temperature, cost target, service interval and exposure duration. |
| Ketone, amine or mixed chemical service | Review the exact chemical first | Standard FKM can fail in several polar media. EPDM may fit some services, but coverage is not universal. | Chemical name, concentration, mixture, temperature and immersion testing. |
Compression Set and Long-Term Leakage
Compression set measures how much permanent deformation remains after the O-ring has been compressed for a specified time and temperature. A seal with excessive set loses contact force and may leak after cooling, pressure cycling or equipment shutdown.
Material names alone do not provide a reliable compression-set ranking. A well-formulated NBR compound can perform consistently at moderate temperature, but results decline as heat exposure approaches its limit. FKM compounds usually retain sealing force better at high temperature. Peroxide-cured EPDM can provide good long-term recovery in water and steam environments.
Ask for compound-level test conditions:
- Compression-set percentage.
- Test temperature and test duration.
- O-ring specimen or standard test button.
- Post-cure condition.
- Results after exposure to the actual operating fluid.
A low percentage from one test cannot be compared directly with a result measured at another temperature or duration. Use the application temperature and required maintenance interval when reviewing the data.
Three Common Material Correction Patterns
These three patterns appear repeatedly during failed-seal reviews. The visible damage helps narrow the cause, but the final decision should still be confirmed with fluid exposure and functional testing.
1. EPDM Used in Mineral Hydraulic Oil
Service condition: Mineral hydraulic oil in a cylinder, pump or valve.
Typical failure: The O-ring becomes larger and softer. Edges may look rounded, and softened rubber can enter the clearance gap. Leakage often increases as pressure cycling continues.
Material correction: Review NBR for moderate oil temperature. Use FKM when oil temperature, fuel exposure or outdoor ozone exceeds the practical range of NBR.
Verification: Immerse the candidate compound in the actual oil, measure volume and hardness change, then run a pressure-cycle test in the production groove.
2. NBR Held at High Oil Temperature
Service condition: Hot lubricating oil or hydraulic oil operating close to or above the continuous limit of the NBR compound.
Typical failure: The rubber hardens, the cross section stays flattened and fine cracks may appear during removal. The assembly can seal while hot and leak after cooling because the O-ring no longer recovers.
Material correction: Review FKM after confirming that the oil, additives and cleaning chemicals are compatible with the selected grade.
Verification: Compare heat aging, compression set and fluid immersion at the actual continuous temperature, followed by repeated hot-and-cold leak testing.
3. Standard FKM Used in an Incompatible Fluid
Service condition: Ketone cleaner, hot amine, selected ester or ether, or unsuitable hot-water and steam exposure.
Typical failure: Swelling, softening, surface blistering or rapid loss of sealing force. Damage can appear sooner than expected because the material was selected from temperature alone.
Material correction: Review EPDM when the main service is water, glycol or compatible polar media without petroleum oil. Aggressive mixed chemicals may require a specialty compound outside NBR, FKM and EPDM.
Verification: Test the exact fluid mixture, concentration and temperature. Include production media, cleaning chemicals and rinse cycles in the same approval plan.
When Paying for an Upgrade Makes Sense
| Current Situation | Recommended Direction | Commercial Reason |
|---|---|---|
| NBR survives the fluid but hardens before the required maintenance interval. | Evaluate FKM. | Longer heat life can reduce shutdowns and labor cost. |
| NBR works indoors but cracks after outdoor storage or field exposure. | Use EPDM for oil-free service or FKM when petroleum media is present. | The material must cover both the internal fluid and the outside environment. |
| EPDM swells in an oil-contaminated water system. | Identify the oil and review NBR or FKM. | A low level of petroleum contamination can control the final material choice. |
| FKM costs more but still swells in the process chemical. | Stop upgrading by price and recheck the chemistry. | A cheaper compatible material can outlast an incompatible premium compound. |
Material price should be compared against replacement labor, downtime, fluid loss, warranty risk and the value of the equipment being protected. NBR remains the right commercial choice when it meets the full service interval. FKM becomes economical when it prevents repeated heat- or fuel-related failures. EPDM often delivers the best value in water and outdoor systems.
For non-O-ring geometries, the same material logic can be applied to custom sealing rings and rubber gaskets, but flange load, gasket thickness and surface finish must also be reviewed.
Selection Checklist for an RFQ
Provide the following information before requesting a material recommendation or price comparison:
- Working media: exact chemical, oil, fuel or coolant name.
- Concentration and mixture: include water content, additives and cleaning chemicals.
- Temperature: minimum, continuous maximum and short peak.
- Pressure: normal pressure, peak pressure and decompression rate.
- Motion: static, reciprocating, oscillating or rotary.
- Seal size: inside diameter, cross section, standard number, drawing or sample.
- Groove information: groove dimensions, clearance and surface finish.
- Hardness: specified Shore A value or open material recommendation.
- Service-life target: operating hours, cycle count or maintenance interval.
- Compliance: FDA, NSF, WRAS, automotive specification or other approval requirements.
Yuefeng supplies custom O-rings in NBR, FKM, EPDM and other compounds. For hydraulic cylinders, pumps and valves, review the available hydraulic O-ring sealing options together with the operating pressure and groove dimensions.
Frequently Asked Questions
Which is better for hydraulic oil, NBR or FKM?
NBR is usually the economical choice for mineral hydraulic oil at moderate temperature. FKM is worth reviewing when the oil temperature, fuel exposure, ozone or required service interval exceeds the practical capability of NBR.
Can EPDM O-rings be used with petroleum oil?
Standard EPDM is generally unsuitable for petroleum oil, hydrocarbon fuel and oil-based grease. Exposure commonly causes swelling, softening and loss of dimensional stability.
Is FKM always the longest-lasting material?
No. FKM can provide long life in hot oil and fuel, but it can fail quickly in an incompatible ketone, amine or steam condition. Service life depends on chemical compatibility, temperature, pressure, motion and seal design.
Which material is best for outdoor water valves?
EPDM is usually the first material to review because it handles water, ozone and weather exposure well. Confirm that petroleum grease or oil will not contact the seal.
Does a higher temperature rating guarantee longer seal life?
No. The fluid may narrow the useful temperature range, and motion, pressure cycling or poor groove design can still cause early failure. Review heat aging and compression-set data in the actual media.
What information is needed to compare NBR, FKM and EPDM pricing?
Send the media, temperature, pressure, motion, O-ring size, hardness, annual quantity, compliance requirement and expected service life. Size alone is not enough for a dependable material comparison.
Compare the Three Materials for Your Application
Share your working media, temperature and expected service life to compare NBR, FKM and EPDM.
Send Application Details
