A rubber seal can be inexpensive, but seal failure can stop an expensive piece of equipment.
A hydraulic cylinder may develop internal leakage. A pump may lose its prime. Oil may leak around a valve stem. Replacing the seal itself may take only a few minutes, but the resulting downtime, cleaning, maintenance, and production loss can cost much more.
In many cases, the problem is not simply poor seal quality. The rubber seal material selection was wrong for the application.
For example, a food equipment customer ran into exactly this. A silicone seal installed in an emulsifying pump swelled and broke down within two weeks. The medium running through the pump was cooking oil combined with a cleaning solvent — and silicone, despite its wide temperature range and food-contact approval, has a well-known weakness against oil, particularly mineral oil and many plant and animal fats. The material grade was correct on paper. It was simply installed in the wrong application.
Selecting a rubber seal material really comes down to one task: translating operating conditions into material properties. So the right approach is not to ask, “Which rubber is the best?” It is to ask, “Which material matches the actual working conditions?” This guide walks through the most common elastomers used in sealing, what each one is actually good at, and how to match a real application to the right choice.
Start With Three Questions Before Choosing the Material
Before comparing rubber materials, define three basic conditions.
1. What Media Will the Seal Contact?
What does the seal actually contact — mineral oil, water, brake fluid, refrigerant, an acid or base, or food product? This is the first filter in material selection, since the same rubber can behave completely differently depending on the fluid, ranging from swelling to embrittlement to outright chemical breakdown.
2. What Is the Operating Temperature?
The number that matters is continuous operating temperature, not an occasional spike. Temperature can change the hardness, elasticity, compression set, and chemical resistance of an elastomer. Most seal failures aren’t mechanical wear — they’re heat failures. Push a material past its rated range, and it either hardens and cracks, or softens and loses its ability to spring back.
3. Is It a Static or Dynamic Seal?
Dynamic seals — rotating shafts, reciprocating piston rods — need wear resistance and low friction. Static seals — flanges, end covers — are judged mainly on compression set and recovery. The same material can perform very differently depending on which category it’s used in.
Six Common Rubber Seal Materials and Their Applications
NBR: A Practical Choice for Oil and Hydraulic Applications
Nitrile rubber, or NBR, is one of the most widely used materials for industrial seals. It handles mineral oil, hydraulic fluid, and lubricants comfortably, performs well from roughly -30°C to 100°C, balances wear resistance and resilience reasonably well, and costs less than almost every alternative on this list.
However, NBR is not suitable for every fluid. Its resistance to ozone and weathering is limited compared with materials such as EPDM or FKM, and compatibility with certain polar solvents and aromatic hydrocarbons can also be problematic.
As a rule of thumb: if the system runs mineral oil under 100°C, NBR is usually the right starting point.
Silicone Rubber (VMQ): Wide Temperature Range With Mechanical Limitations
Silicone’s defining strength is its temperature range, comfortably spanning -60°C to 200°C, combined with strong ozone resistance, biological inertness, and readily available FDA food-grade formulations. That combination makes it common in food, medical, and electronic sealing applications.
However, tensile strength runs at roughly half of NBR’s, wear resistance is weak, and it has essentially no place in dynamic sealing. It also doesn’t tolerate oil well — mineral oil causes noticeable swelling, and contact with fatty foods shortens its service life considerably.
As a rule of thumb: choose it for temperature extremes, food contact, or electrical insulation — not for oil or wear resistance.
FKM: For High Temperature, Oil, and Chemical Resistance
FKM functions as an upgraded version of NBR across nearly every dimension. Continuous service temperature extends past 200°C; it resists mineral oil, fuel, and a wide range of acids and bases, and its aging resistance is among the best of any elastomer. It is commonly used in engines, turbines, chemical pumps, and downhole oilfield equipment.
However, the cost is typically several times the price of NBR. Standard grades also don’t handle cold well, stiffening noticeably around -20°C, and it has known weaknesses against ketones, esters, and prolonged exposure to hot steam or hot water.
As a rule of thumb: high temperature, mixed or aggressive media, and a budget that supports reliability point straight to FKM.
EPDM: A Common Choice for Water, Steam, and Outdoor Applications
EPDM resists ozone and aging well, handles hot water and steam, and tolerates glycol-based brake fluids such as DOT3 and DOT4. That profile makes it standard in automotive radiators, heater hoses, and brake systems, and it’s a common choice for outdoor weatherstripping that needs to last a decade without cracking.
However, its limitation is oil. Contact with mineral oil causes it to swell and soften, and installing it in an oil-contact application by mistake produces failure fast enough to catch attention immediately.
As a rule of thumb: default to EPDM for water, steam, brake fluid, or outdoor weathering — and keep it away from oil entirely.
HNBR: Upgraded NBR
HNBR is produced by saturating the double bonds in NBR’s molecular structure through hydrogenation. It keeps NBR’s oil resistance while pushing the usable temperature range up to around 150°C, along with meaningfully better wear resistance and ozone resistance.
As a rule of thumb: reach for it when both temperature and oil resistance need to step up a level from NBR, without moving all the way to fluoroelastomer pricing.
PTFE: Chemical Resistance Without Elastomeric Recovery
PTFE is technically a fluoropolymer rather than a rubber elastomer, but it is an important sealing material for demanding chemical applications. It resists nearly every chemical, functions from -200°C to 260°C, and has an exceptionally low coefficient of friction — properties that make it essential in strongly corrosive chemical processing environments.
However, compressed PTFE doesn’t spring back on its own, so it can’t function as a standard O-ring by itself. In practice, it’s usually built into a spring-energized seal or used as an encapsulating layer around a rubber O-ring.
As a rule of thumb: reach for it against strong acids, strong bases, and aggressive solvents, but not where compression recovery is required on its own.
Quick Reference of Rubber Materials Selection
| Material | Typical Temp Range | Oil Resistance | Key Strength | Key Weakness |
|---|---|---|---|---|
| NBR | -30°C to 100°C | Good | Cost, balance of wear and resilience | Poor ozone/UV resistance |
| Silicone (VMQ) | -60°C to 200°C | Poor | Temperature range, food/medical grades | Low strength and wear resistance |
| FKM | Up to 200°C+ | Excellent | Heat and broad chemical resistance | Cost, poor cold flexibility |
| EPDM | Wide, water/steam-stable | Poor | Water, steam, weathering | Fails quickly in oil |
| HNBR | Up to ~150°C | Very good | Wear and temperature upgrade over NBR | Cost above standard NBR |
| PTFE | -200°C to 260°C | Excellent | Chemical inertness | No elastic recovery |
A Simple Rubber Seal Material Selection Process
Take a common hydraulic cylinder O-ring as an example.
The medium is mineral-based hydraulic fluid, which eliminates EPDM and silicone immediately. Shop-floor temperatures typically run 70–80°C, well within NBR’s range. The rod moves reciprocally, and NBR’s wear resistance holds up fine here. The answer is NBR 70A — nitrile rubber at 70 durometer, the standard specification format for hydraulic seals.
Move that same cylinder next to a furnace, with oil temperatures regularly running above 150°C, and NBR is no longer sufficient. FKM or HNBR becomes the right call, and this isn’t the place to cut costs to save a few dollars per seal.
A water pump end cover tells a different story. The medium is water, with no oil contact, which makes EPDM the more cost-effective choice — it also tolerates residual chlorine in the water supply better than NBR does over time. Many buyers default to NBR out of habit, and it will technically work, but EPDM typically lasts considerably longer in this specific environment.
A rotary shaft seal running at meaningful speed, lubricated by grease, needs a material that balances wear resistance, temperature tolerance, and oil resistance simultaneously. FKM or HNBR are the usual answers here, with the final choice depending on actual operating temperature and shaft speed.
Four Common Mistakes in Rubber Seal Material Selection
1. Choosing Material by Color
Color is not a reliable way to identify rubber. Most FKM is black, but so is most NBR, and silicone comes in essentially any color a customer wants. Color is set by pigment, not polymer chemistry. The purchase specification should identify the actual material and required compound or grade.
2. Treating Silicone as a Universal High-Temperature Seal
Silicone has excellent temperature and weathering properties, but that does not make it suitable for every high-temperature application. Its oil resistance, abrasion resistance, tensile strength, and tear resistance must also be considered.
3. Comparing Only the Unit Price
NBR may cost considerably less than FKM, but material price is only one part of the total cost. If an inexpensive seal fails frequently and causes equipment downtime, maintenance, cleaning, or product loss, the lowest purchase price may not result in the lowest operating cost. Material selection should therefore consider expected service life and failure consequences, not just the price of one seal.
4. Choosing Only by Size and Ignoring Hardness
Two seals with the same dimensions can have different hardness ratings. Shore A hardness affects installation, extrusion resistance, sealing force, and deformation behavior. A seal that is too soft or too hard for the groove and operating pressure may not perform correctly. Material, hardness, seal geometry, groove design, pressure, and clearance should be considered as a complete sealing system.
Conclusion
No single rubber material fits every sealing application — the right choice depends on the operating conditions, not the other way around.
- Mineral oils, general hydraulic systems → NBR (practical starting point)
- Higher temperature, aging, or mechanical demands → HNBR or FKM
- Water, steam, outdoor exposure → EPDM
- Wide temperature range, flexibility, weather resistance, insulation → Silicone
- Highly aggressive chemicals → PTFE or other specialized materials (technically a fluoropolymer, not a rubber, but often used where rubber options fall short)
Tell us your media, temperature range, pressure, movement type, and hardness requirement — Flexiparts will help confirm the right material and manufacturing process for your application.
