O-Ring Material Selection: NBR, FKM, EPDM, and Silicone Compared

Why Material Selection Matters

An O-ring’s performance is determined by its ability to maintain elasticity and sealing force under operating conditions. When exposed to incompatible fluids or excessive temperatures, elastomers can swell, harden, crack, or degrade, leading to leakage and system failure. Selecting the wrong material may result in:

• Premature seal failure and unplanned downtime

• Fluid contamination and environmental hazards

• Increased maintenance costs

• Safety risks in critical applications

Therefore, understanding the strengths and limitations of each material is essential for reliable sealing.

Common O-Ring Materials: Properties and Applications

1. NBR (Nitrile Rubber / Buna-N)

NBR is the most widely used O-ring material due to its excellent oil and fuel resistance at a low cost.

Key Properties:

• Temperature range: -30°C to +100°C (short-term up to +120°C)

• Excellent resistance to petroleum-based oils, greases, and hydraulic fluids

• Good mechanical strength and abrasion resistance

• Poor resistance to ozone, ketones, and strong acids

Typical Applications:

• Hydraulic systems, automotive engines, gearboxes

• General industrial sealing where oil resistance is required

• Water and air systems (not recommended for steam)

2. FKM (Fluoroelastomer / Viton®)

FKM offers superior heat and chemical resistance compared to NBR, making it suitable for demanding environments.

Key Properties:

• Temperature range: -20°C to +200°C (special grades up to +250°C)

• Excellent resistance to oils, fuels, acids, and many solvents

• Good compression set and aging resistance

• Poor resistance to amines, ketones, and hot water/steam

Typical Applications:

• Automotive fuel systems, chemical processing equipment

• High-temperature hydraulic systems

• Aerospace and defense applications

3. EPDM (Ethylene Propylene Diene Monomer)

EPDM is known for its outstanding water and steam resistance, as well as good weather resistance.

Key Properties:

• Temperature range: -40°C to +150°C (special grades up to +175°C)

• Excellent resistance to water, steam, and glycol-based fluids

• Good ozone and UV resistance

• Poor resistance to petroleum oils and hydrocarbons

Typical Applications:

• Water and wastewater systems, brake systems (non-petroleum)

• HVAC equipment, outdoor applications

• Steam and hot water sealing

4. Silicone (VMQ)

Silicone rubber offers an exceptionally wide temperature range and good flexibility at low temperatures.

Key Properties:

• Temperature range: -60°C to +200°C (special grades up to +250°C)

• Excellent low-temperature flexibility

• Good electrical insulation properties

• Moderate resistance to oils and fuels (not recommended for dynamic oil sealing)

Typical Applications:

• Food and pharmaceutical processing (FDA grades)

• Medical devices, electrical enclosures

• Aerospace and high-temperature air systems

5. Other Materials (Brief Overview)

• PTFE (Polytetrafluoroethylene): Exceptional chemical inertness, wide temperature range (-200°C to +260°C), low friction, but lacks elasticity; often used with spring energizers.

• FFKM (Perfluoroelastomer): Ultimate chemical and thermal resistance (up to +300°C), but very high cost; used in semiconductor and chemical processing.

• PU (Polyurethane): High wear and extrusion resistance, good for high-pressure hydraulic applications, but limited temperature range.

Material Comparison Table

Key Selection Criteria

When choosing an O-ring material, consider the following factors:

1. Operating Temperature: Continuous and peak temperatures must fall within the material’s limits.

2. Chemical Compatibility: The elastomer must resist swelling or degradation from the contact fluid.

3. Pressure: High-pressure systems may require harder compounds or backup rings.

4. Dynamic vs. Static: Dynamic applications demand materials with low friction and high wear resistance.

5. Regulatory Requirements: Food, medical, and aerospace applications may require FDA, USP Class VI, or other approvals.

6. Cost: While performance is paramount, material cost should be balanced against service life and maintenance savings.

Installation and Storage Best Practices

Even the best material can fail if not handled properly. Follow these guidelines:

• Inspect O-rings for cuts, nicks, or contamination before installation.

• Lubricate with a compatible lubricant to prevent damage during assembly.

• Avoid stretching O-rings beyond recommended limits.

• Store in a cool, dark, and dry environment away from ozone sources.

• Observe shelf life and rotate stock accordingly.

Conclusion

Selecting the correct O-ring material is a critical decision that directly impacts equipment reliability and maintenance costs. NBR remains the cost-effective choice for general oil-resistant applications, while FKM excels in high-temperature and chemically aggressive environments. EPDM is ideal for water and steam service, and Silicone offers unmatched low-temperature flexibility. For extreme chemical and thermal demands, PTFE and FFKM provide ultimate performance at a premium.

By understanding the properties and limitations of each material, engineers can optimize sealing performance and extend the service life of their equipment. FOREVER SEALS offers a full range of O-rings in NBR, FKM, EPDM, Silicone, PTFE, and other materials, with standard and custom sizes available. Contact our technical team for assistance in selecting the right O-ring for your application.