O-Ring Materials Guide

O-Ring Materials Guide: How to Choose the Right Compound for Your Application

Published by Mutual Screw & Supply — Serving Manufacturers and Industry Since 1947

An O-ring failure isn't just an inconvenience — it can mean a leaking hydraulic system, contaminated process fluid, a shutdown production line, or a failed regulatory inspection. In most cases, the seal itself isn't the problem. The wrong material is.

O-rings are manufactured in a wide range of elastomers and polymers, each engineered for specific combinations of temperature, chemical exposure, pressure, and application environment. Choosing the right compound is every bit as important as choosing the right size.

At Mutual Screw & Supply, we stock O-rings in the most widely specified industrial materials — all with certifications included — so you can seal with confidence. This guide breaks down the most common O-ring materials, what makes each one unique, and how to match the right compound to your application.

What Is an O-Ring?

An O-ring is a torus-shaped elastomeric seal designed to be seated in a groove and compressed between two mating surfaces, creating a leak-proof barrier against liquids or gases. They're used in virtually every industry — hydraulics, pneumatics, fluid processing, automotive, aerospace, food and beverage, pharmaceuticals, and more.

The AS568 standard (maintained by SAE International) defines the most common inch-series O-ring sizes used in North America. O-rings are also available in metric sizes for equipment manufactured to ISO or DIN standards.

Size is just one variable. The compound — the elastomeric material the O-ring is made from — determines whether it will hold up or fail the moment it contacts the fluids, temperatures, and pressures of your application.

The Most Common O-Ring Materials

1. Buna-N (Nitrile / NBR) — The Everyday Workhorse

Best for: Petroleum-based oils, hydraulic fluids, fuels, water, general industrial use Temperature range: -40°F to +250°F (-40°C to +121°C) Not recommended for: Ozone, UV exposure, ketones, esters, strong acids

Buna-N (also called Nitrile or NBR) is the most widely used O-ring material in the world, and for good reason. It offers an excellent balance of cost, mechanical performance, and chemical resistance to the fluids most commonly found in industrial and manufacturing environments — petroleum oils, mineral-based hydraulic fluids, LP gas, propane, diesel, water, and most common lubricants.

If you're running a hydraulic cylinder, pneumatic tool, fuel system, or standard MRO application with no unusual chemical exposure, Buna-N is almost always your default choice. It's reliable, cost-effective, and available in the widest range of AS568 standard sizes.

Where Buna-N falls short is outdoor weathering. Exposure to ozone, UV radiation, sunlight, and ketone-based solvents will degrade the compound over time. For applications that live outdoors or involve aggressive chemical exposure, you'll want to step up to one of the materials below.

Shop Buna-N O-Rings at Mutual Screw →

2. Viton® (Fluorocarbon / FKM) — The High-Performance Standard

Best for: Fuels, acids, solvents, aggressive chemicals, high-temperature environments Temperature range: -15°F to +400°F (-26°C to +204°C) Not recommended for: Ketones, esters, ammonia, low-temperature applications below -15°F

Viton is the go-to material when Buna-N isn't enough. Developed by DuPont (now Chemours), Viton is a fluoroelastomer that delivers exceptional resistance to a wide range of aggressive fuels, acids, aromatic hydrocarbons, and chemical solvents — along with the highest continuous temperature rating of any standard elastomeric O-ring material.

If your application involves gasoline, diesel, biodiesel, hydraulic fluid at elevated temperatures, concentrated acids, or any environment where Buna-N has failed prematurely, Viton is the logical upgrade. It's the dominant material choice in aerospace fuel systems, automotive fuel handling, chemical processing equipment, and industrial machinery operating at sustained elevated temperatures.

Viton O-rings are typically brown or black in color. The brown Viton (fluoroelastomer) variants are particularly common in hard-service industrial applications.

One trade-off: Viton's lower temperature limit of around -15°F means it's not the right choice for cryogenic or extreme cold-weather applications.

Shop Brown Viton O-Rings at Mutual Screw →

3. Silicone (VMQ) — Temperature Extremes and Food-Safe Applications

Best for: High/low temperature extremes, food and beverage, medical/pharmaceutical, static seals, outdoor exposure Temperature range: -85°F to +450°F (-65°C to +232°C) Not recommended for: Dynamic sealing applications, petroleum oils, fuels, steam

Silicone O-rings excel where temperature flexibility is the primary concern. With one of the broadest operating temperature ranges of any O-ring material — from extreme cold to sustained high heat — silicone is the right choice when the application routinely moves through wide thermal cycles or operates at temperature extremes that would crack or harden other elastomers.

Silicone also has excellent resistance to ozone, UV, oxygen, and weathering, making it well-suited for outdoor equipment and applications with long service intervals. Food-grade silicone formulations meet FDA requirements, making them a common choice in food processing equipment, water filtration systems, medical devices, and pharmaceutical manufacturing.

The important limitation of silicone is mechanical strength. It has relatively low tensile strength and poor abrasion resistance, which makes it a poor performer in dynamic (moving) sealing applications. For static face seals, pipe fittings, and gasketing applications where the O-ring sits still, silicone performs excellently.

Shop Silicone O-Rings at Mutual Screw →

4. PTFE (Polytetrafluoroethylene / Teflon®) — Maximum Chemical Resistance

Best for: Aggressive acids, bases, solvents, pharmaceutical, semiconductor, chemical processing Temperature range: -100°F to +500°F (-73°C to +260°C) Not recommended for: High-pressure dynamic applications (PTFE has low elasticity), applications requiring compression resilience

PTFE O-rings — often referred to by the DuPont trade name Teflon® — represent the top of the pyramid for chemical resistance. PTFE is chemically inert, meaning it is resistant to virtually all known acids, bases, solvents, and aggressive fluids. There is almost no chemical that will attack it.

Combine that chemical inertness with a temperature range spanning from -100°F to +500°F, and you have a material that's specified wherever extreme conditions make all other options inadequate. PTFE is the standard choice in pharmaceutical manufacturing (where extractables and reactivity are tightly controlled), semiconductor fabrication (where ultra-pure process fluids can't be contaminated by the seal), and chemical processing lines handling concentrated acids, caustics, and solvents.

One important caveat: PTFE is not an elastomer — it is a thermoplastic. This means it doesn't compress and spring back the way rubber-based O-rings do. PTFE O-rings require precise groove design and proper installation to seal correctly, and they are best suited for static or low-movement sealing applications.

Shop Ultra Chemical Resistant PTFE O-Rings at Mutual Screw →

5. HNBR (Hydrogenated Nitrile) — Upgraded Nitrile for Demanding Conditions

Best for: Oil and gas, refrigerants, steam, sour gas (H2S), automotive AC systems, harsh mechanical applications Temperature range: -40°F to +300°F (-40°C to +149°C) Not recommended for: Aromatic hydrocarbons, chlorinated solvents, polar solvents

HNBR is the upgraded version of Buna-N, produced by hydrogenating (adding hydrogen to) standard nitrile rubber to saturate the double bonds in the polymer chain. The result is a material that retains nitrile's excellent oil resistance while adding significantly better heat resistance, ozone resistance, and mechanical toughness.

HNBR is the standard sealing material in automotive air conditioning systems because of its compatibility with modern HFC refrigerants (R-134a, R-1234yf). It's also widely used in oil and gas applications involving sour gas (hydrogen sulfide), geothermal systems, and any environment where a standard Buna-N O-ring holds up under normal conditions but begins to fail when temperatures rise or the chemical environment becomes more aggressive.

Think of HNBR as the right choice when Buna-N almost works — but not quite.

Shop HNBR O-Rings at Mutual Screw →

6. Neoprene (Chloroprene / CR) — The Outdoor and Refrigerant Specialist

Best for: Refrigerants, outdoor weathering, moderate chemical exposure, marine environments Temperature range: -40°F to +250°F (-40°C to +121°C) Not recommended for: Aromatic hydrocarbons, ketones, strong acids

Neoprene is one of the oldest synthetic rubbers and remains a strong choice for specific applications where it genuinely outperforms the alternatives. Its two standout properties are excellent resistance to ozone and weathering, and good compatibility with older chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) refrigerants.

Neoprene also performs well in marine environments, with moderate resistance to seawater and good flexibility across a wide temperature range. It's a common seal material in HVAC equipment, refrigeration systems, and outdoor industrial enclosures.

That said, Neoprene's chemical resistance profile is narrower than Viton and its mechanical properties are not as strong as HNBR. It's most useful when you specifically need ozone/weather resistance combined with refrigerant compatibility, rather than as a general-purpose upgrade from Buna-N.

Shop Neoprene O-Rings at Mutual Screw →

Quick-Reference: O-Ring Material Comparison

Material Temp Range Oil/Fuel Chemicals Weather/Ozone Best Use
Buna-N (NBR) -40°F to +250°F Excellent Moderate Poor General industrial, hydraulics
Viton (FKM) -15°F to +400°F Excellent Excellent Good High-temp, aggressive fuels/chemicals
Silicone (VMQ) -85°F to +450°F Poor Moderate Excellent Temperature extremes, food/medical
PTFE -100°F to +500°F Excellent Excellent (broadest) Excellent Pharmaceutical, semiconductor, chemical
HNBR -40°F to +300°F Excellent Good Good Refrigerants, sour gas, auto AC
Neoprene (CR) -40°F to +250°F Moderate Moderate Excellent Refrigerants, marine, outdoor HVAC

How to Choose the Right O-Ring Material

When selecting an O-ring compound, work through these four questions:

1. What fluids or chemicals will the O-ring contact? This is the most important variable. A Buna-N O-ring will swell and fail in ketone-based solvents. A Viton O-ring will crack in ammonia. Always verify chemical compatibility before committing to a material.

2. What are the operating temperatures? Both the continuous service temperature and any peak or transient temperatures matter. A material rated to +250°F will hold up in daily use but may fail under a brief temperature spike if that spike routinely hits +350°F.

3. Is this a static or dynamic application? Dynamic seals (pistons, rods, shafts in motion) require materials with strong mechanical properties and good abrasion resistance — Buna-N, Viton, and HNBR are better choices here than Silicone or PTFE. Static seals (face seals, pipe connections, covers) can use a broader range of materials.

4. Are there compliance requirements? Pharmaceutical, food and beverage, aerospace, and military applications often carry specific material compliance requirements (FDA, USP Class VI, MIL-SPEC). Our O-rings come with certifications included in each pack — confirm requirements before ordering for regulated applications.

Why Material Certifications Matter

In manufacturing and industrial environments, O-ring material certification is often non-negotiable — especially in aerospace, defense, pharmaceutical, and food processing applications. A certificate of conformance (C of C) documents the material composition, lot traceability, and compliance to applicable standards.

At Mutual Screw & Supply, every O-ring pack we ship includes a certification. That's not a standard practice across the industry — and it matters when your customer, your quality department, or your regulatory body asks for documentation.

Browse All O-Rings at Mutual Screw

We stock O-rings in AS568 standard and metric sizes across all major compounds, with certifications included in every pack. Whether you need a single compound in bulk or want to stock a mixed assortment, we can help.

Need help selecting the right compound for a specific application? Call us at 1-800-222-0324 or email sales@mutualscrew.com — we've been matching the right fasteners and seals to the right applications since 1947.

It's Better When It's Mutual.

Mutual Screw & Supply 68 West Passaic Street, Rochelle Park, NJ 07662 Toll Free: 800-222-0324 | Local: 201-845-5700 www.mutualscrew.com

Material data shown is for general reference only. Always verify chemical compatibility and temperature ratings with the manufacturer for critical applications. O-ring performance varies by specific compound formulation, groove design, and installation conditions.