NBR vs EPDM O-Rings: Oil Sealing vs Water & Steam
NBR (Nitrile) and EPDM (Ethylene Propylene Diene Monomer) are the two most commonly specified general-purpose O-ring materials. They are often similar in price, yet they are chemically incompatible with each other’s primary fluids. Choosing the wrong one is one of the most frequent causes of seal failure in industrial maintenance. This guide provides a detailed comparison to help you select the right material.
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Key Differences at a Glance
| Property | NBR (Nitrile) | EPDM |
|---|---|---|
| Temperature range | -40°C to +120°C | -50°C to +150°C |
| Petroleum oil resistance | Excellent | Poor (swells rapidly) |
| Water / steam resistance | Fair to 100°C | Excellent to 150°C |
| Ozone / UV resistance | Poor | Excellent |
| Cost index | 1 (baseline) | 1.5–2× |
| Tensile strength | High (15–25 MPa) | Moderate (10–20 MPa) |
| Abrasion resistance | Good | Fair |
| Best for | Hydraulic oil, fuel, grease | Water, steam, brake fluid, outdoor |
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Fluid Compatibility: The Deciding Factor
The simplest rule is this:
- If the fluid is petroleum-based → choose NBR.
- If the fluid is water, steam, glycol, or brake fluid → choose EPDM.
EPDM swells dramatically in contact with mineral oils, hydraulic fluids, gasoline, and diesel. A standard EPDM O-ring submerged in hydraulic oil can double in volume and lose all mechanical strength within days.
Conversely, NBR is not recommended for hot water or steam above 100°C. It will harden and develop compression set more quickly than EPDM under sustained hot-water exposure.
| Fluid Type | NBR Rating | EPDM Rating | Winner |
|---|---|---|---|
| Mineral hydraulic oil | Excellent | Poor | NBR |
| Gasoline / diesel | Excellent | Poor | NBR |
| Water (ambient) | Fair | Excellent | EPDM |
| Hot water (>80°C) | Poor | Excellent | EPDM |
| Saturated steam | Poor | Excellent | EPDM |
| Glycol brake fluid (DOT 3/4) | Poor | Excellent | EPDM |
| Silicone brake fluid (DOT 5) | Varies | Poor | Consult us |
| Alcohols | Fair | Good | EPDM |
| Ketones / esters | Poor | Fair | Neither — use FKM or FFKM |
Temperature Comparison
EPDM has a slight advantage at both ends of the scale:
- Cold limit: EPDM to -50°C vs NBR to -40°C. For outdoor refrigeration or arctic service, EPDM may be the better choice if oils are not present.
- Hot limit: EPDM to +150°C vs NBR to +120°C. For hot water and low-pressure steam, EPDM is the clear winner.
If temperatures exceed +120°C in oil service, neither material is suitable — upgrade to FKM.
Weather and Ozone Resistance
NBR has poor resistance to ozone, UV radiation, and outdoor weathering. Ozone cracking appears as fine surface cracks perpendicular to the stress axis and is a common failure mode for NBR seals used outdoors or near electrical equipment.
EPDM has outstanding ozone and UV resistance. It is the standard material for outdoor water systems, solar thermal installations, and any application exposed to atmospheric aging.
Choose EPDM for: outdoor HVAC, water treatment, building services, and automotive cooling systems. Choose NBR for: indoor hydraulic and fuel systems where ozone exposure is minimal.
Mechanical Properties
NBR generally has higher tensile strength and better abrasion resistance than EPDM. This makes NBR the better choice for dynamic reciprocating seals in hydraulic cylinders, where the O-ring slides against a metal surface.
EPDM has moderate mechanical properties and is perfectly adequate for static seals. For dynamic applications in water or glycol, special EPDM compounds with improved wear resistance are available.
| Property | NBR | EPDM |
|---|---|---|
| Hardness range | 40–90 Shore A | 40–90 Shore A |
| Tensile strength | 15–25 MPa | 10–20 MPa |
| Elongation at break | 200–500% | 200–400% |
| Compression set (100°C) | 15–25% | 20–35% |
| Tear strength | Good | Moderate |
Brake Fluid Compatibility
Automotive brake fluids (DOT 3, DOT 4, DOT 5.1) are glycol-based. NBR is incompatible with glycol brake fluids and will swell.
EPDM is the correct material for brake system O-rings, master cylinders, and ABS modulators in glycol-fluid systems.
Exception: DOT 5 silicone brake fluid requires specially formulated compounds — consult us for the correct grade.
Cost Considerations
Standard NBR is the lowest-cost general-purpose O-ring material. EPDM is slightly more expensive, but the price difference is small compared to the cost of a seal failure.
The real cost penalty comes from misapplication: using EPDM in oil, or NBR in hot steam, leads to downtime, leakage, and premature replacement that far outweigh any material savings.
When to Choose NBR
- Hydraulic systems with mineral oil-based fluids
- Fuel handling, gasoline, diesel, and biodiesel blends
- Pneumatic systems with petroleum-based lubricators
- General industrial oil seals where temperature stays below +120°C
- Dynamic reciprocating seals requiring abrasion resistance
When to Choose EPDM
- Hot water, steam, and boiler systems up to +150°C
- Automotive cooling systems and glycol-based brake fluids
- Outdoor HVAC, water treatment, and plumbing
- Food-grade water contact (FDA / NSF 61 certified grades)
- Applications requiring ozone and UV resistance
- Steam sterilisation (autoclave) applications
What If You Need Both Oil and Water Resistance?
If the seal must contact both petroleum oil and water regularly, neither NBR nor EPDM is ideal:
- HNBR offers good oil resistance with improved hot water tolerance up to +120°C.
- FKM resists oils and has fair water resistance up to +100°C.
- FFKM handles virtually everything but at a significantly higher cost.
Contact us with the full fluid list, temperature range, and application type for a tailored recommendation.
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Frequently Asked Questions
Can I use EPDM for hydraulic oil? No. Standard EPDM swells rapidly in petroleum-based hydraulic oils. There are specialty EPDM compounds with improved oil resistance, but they do not match NBR performance and are not recommended for standard hydraulic service.
Is NBR safe for drinking water? Standard NBR is not certified for potable water contact. For drinking water systems, use NSF 61 certified EPDM or VMQ (Silicone).
Which is better for outdoor use — NBR or EPDM? EPDM is far superior for outdoor use due to its ozone and UV resistance. NBR will crack and harden when exposed to sunlight and atmospheric ozone.
Can NBR handle steam? NBR can handle intermittent hot water up to approximately 100°C, but it is not recommended for continuous steam service. EPDM is the standard elastomer for steam sealing.
What if my application sees both oil and water? If the seal must contact both petroleum oil and water regularly, consider HNBR (hydrogenated nitrile) or FKM, depending on temperature. Contact us with the full fluid list for a recommendation.
Does NBR or EPDM last longer? In the correct fluid environment, both materials can last many years. In the wrong environment, both can fail within days. Material selection based on fluid compatibility is the primary determinant of seal life.