Buna-N (Nitrile) vs EPDM Rubber
Buna-N and EPDM are near-mirror images. Buna-N, also called nitrile or NBR, is the oil-service standard: it resists petroleum oils, fuels, and hydraulic fluids but cracks quickly outdoors. EPDM is the opposite: it excels in weather, water, and steam but swells and fails in oil. The choice almost always comes down to one question: is there petroleum contact, or is there outdoor and water exposure?
Because they are both low-cost commodity elastomers, they are the two most common candidates for everyday gaskets, seals, and o-rings. This guide compares them property by property so you specify the right one the first time. Wayne Rubber molds both materials at our Wixom, Michigan plant.
Quick Comparison
| Property | Buna-N (Nitrile / NBR) | EPDM |
|---|---|---|
| Petroleum oil, fuel, hydraulic fluid | Excellent | Poor. Swells and degrades |
| Water, steam and glycol coolant | Fair | Excellent |
| Ozone, UV and weathering | Poor. Cracks outdoors | Excellent |
| Continuous service temperature | -40°C to +120°C (ACN dependent) | -40°C to +150°C |
| Low temperature flexibility | Good (low-ACN grades) | Excellent |
| Brake fluid (glycol based) | Poor | Excellent |
| Abrasion resistance | Very good | Good |
| Compression set | Good | Very good (peroxide cured) |
| Relative compound cost | Low | Low |
| Typical hardness range | 40 to 90 Shore A | 40 to 90 Shore A |
The Two Materials
What Is Buna-N (Nitrile / NBR) Rubber?
Buna-N is a copolymer of acrylonitrile and butadiene, which is why it is also called nitrile or NBR. It is the most widely used sealing elastomer in the world because it combines strong oil and fuel resistance with good mechanical strength at low cost. Its defining specification variable is acrylonitrile (ACN) content, which ranges from about 18 to 50 percent: higher ACN improves oil and fuel resistance, lower ACN improves low-temperature flexibility, and most general-purpose grades sit near 33 percent. Its weakness is the outdoors, where ozone and UV crack it within months. Full detail is on the nitrile (NBR) material page.
What Is EPDM Rubber?
EPDM (ethylene propylene diene monomer) has a fully saturated backbone that resists ozone, UV, and oxidation, making it the benchmark for outdoor, water, and steam service. It does not swell in water and stays flexible at low temperatures. Its hard limit is petroleum: oils and fuels destroy it. See the EPDM rubber material page for grades and data.
Property by Property
Oil, Fuel and Hydraulic Fluid
This is the reason Buna-N exists. Nitrile resists petroleum oils, fuels, and hydraulic fluids, which makes it the default for engine, fuel-system, and hydraulic sealing. EPDM swells and fails on contact with these fluids. If petroleum is present in any form, EPDM is off the table and Buna-N is the starting point.
Weathering, Ozone and UV
The mirror image. EPDM is essentially immune to ozone and UV and lasts for years outdoors, while standard nitrile cracks in high-ozone or sunlit environments within months. For an outdoor part, EPDM wins unless oil is also present, in which case a nitrile blend, neoprene, or HNBR is the better route.
Water, Steam and Brake Fluid
EPDM again. It is the standard for water, steam, glycol coolant, and glycol-based brake fluids, all of which nitrile handles only poorly. This is why cooling-system and brake seals are usually EPDM even though nitrile dominates elsewhere in a vehicle.
Temperature and ACN Trade-Off
EPDM carries a slightly higher continuous ceiling, near 150°C versus about 120°C for standard nitrile. Within nitrile, ACN content sets the balance: higher ACN buys oil resistance at the cost of cold flexibility, lower ACN does the reverse. For hot-oil service beyond nitrile’s limit, HNBR is the upgrade path.
Abrasion, Compression Set and Cost
Nitrile has an edge in abrasion resistance; peroxide-cured EPDM has an edge in compression set for long-life static seals. Both are among the most economical elastomers, so cost rarely decides between them. The environment does.
Typical Applications
Choose Buna-N (nitrile) for: fuel-system and engine o-rings and gaskets, hydraulic seals, oil-service diaphragms, and any part contacting petroleum oils, fuels, or lubricants.
Choose EPDM for: coolant and water-system seals and hoses, gaskets and seals in water or steam service, weatherstripping and outdoor sealing, HVAC gaskets, and brake-fluid seals.
How to Choose in 30 Seconds
- Is there petroleum oil, fuel, or hydraulic fluid? Yes: Buna-N (nitrile).
- Is it water, steam, coolant, or glycol brake fluid? Yes: EPDM.
- Is the part outdoors or ozone-exposed with no oil? EPDM.
- Both oil and outdoor exposure at once? Consider neoprene, an NBR/PVC blend, or HNBR.
- Hot oil above nitrile’s limit? Step up to HNBR or FKM.
- Unsure of the fluids? Send us the operating conditions and drawing. We will recommend the material and, for nitrile, the ACN grade. Contact Wayne Rubber.
Frequently Asked Questions
Is Buna-N the same as nitrile?
Yes. Buna-N, nitrile, and NBR are three names for the same material, a copolymer of acrylonitrile and butadiene. The names are used interchangeably on drawings and datasheets.
Is nitrile or EPDM better for oil?
Nitrile (Buna-N), by a wide margin. It resists petroleum oils, fuels, and hydraulic fluids, while EPDM swells and degrades in them. For any petroleum contact, use nitrile, not EPDM.
Which is better outdoors, nitrile or EPDM?
EPDM. It resists ozone and UV and lasts for years outdoors, while standard nitrile cracks in sunlight and high-ozone environments within months. For outdoor parts that also see oil, consider neoprene or an NBR/PVC blend.
Can EPDM be used with oil or fuel?
No. EPDM swells and loses its properties in petroleum oils and fuels. Use nitrile (Buna-N) for oil and fuel service, HNBR for hot oil, or FKM for fuels combined with high heat or aggressive chemicals.
What does ACN content mean for nitrile?
ACN (acrylonitrile) content, roughly 18 to 50 percent, sets nitrile’s balance of properties. Higher ACN improves oil and fuel resistance but reduces low-temperature flexibility; lower ACN does the reverse. Most general-purpose nitrile runs near 33 percent ACN.
Nitrile or EPDM? Let Us Confirm the Right One
Send us the fluids, temperature, and drawing, and our engineers will recommend the material and, for nitrile, the ACN grade to match your application. In-house nitrile compounding and molding from our Wixom, Michigan plant.
Request a Material Recommendation