Butterfly Valve Seat Materials: EPDM, NBR, PTFE, Viton and Metal Seat Comparison

Choosing the right butterfly valve seat material is one of the fastest ways to prevent leakage, swelling, high torque, premature wear and unnecessary maintenance. The seat is the part that touches the disc and the media, so it must match the fluid, temperature, pressure, certification requirements and expected service life.

This guide compares the most common butterfly valve seat materials: EPDM, NBR, PTFE, Viton/FKM and metal seats. It is written for engineers, distributors and procurement teams who need a practical material selection reference before sending an RFQ or approving a valve datasheet.

What does a butterfly valve seat do?

A butterfly valve seat forms the sealing surface between the valve body and the rotating disc. When the disc closes, it presses against the seat to stop flow. The seat also helps control operating torque, compensate for small installation deviations and protect the valve body from direct media contact in lined designs.

For soft-seated butterfly valves, sealing depends mainly on the elastic deformation of rubber or PTFE. For metal-seated butterfly valves, sealing depends more on machined metal contact, disc offset design and pressure-assisted geometry. That is why the same valve size can behave very differently when the seat material changes.

For a broader explanation of seat structures, see our butterfly valve seat types and selection guide.

Butterfly valve seat material comparison table

The table below gives a practical first-pass comparison. Final selection should always be checked against the actual medium concentration, operating temperature, pressure, flow velocity, seat design and required certifications.

Engineering note: API Standard 609 covers butterfly valve design, materials, face-to-face dimensions, pressure-temperature ratings, and inspection/test requirements for several butterfly valve body materials and configurations. It is a valve standard, not a chemical compatibility chart, so seat material selection still needs a separate media compatibility review.

When should you choose EPDM butterfly valve seats?

Choose EPDM when the system mainly handles water-based media and needs stable sealing at a reasonable cost. EPDM is widely used in waterworks valves, HVAC, chilled water, general wastewater and potable water projects when the exact compound has the correct drinking-water approval.

EPDM performs well with water, steam, dilute acids, dilute alkalis, ozone and weather exposure. That makes it a practical default for many resilient seated butterfly valves. However, EPDM should not be used for mineral oil, diesel, gasoline or most hydrocarbon media because swelling and seal loss can occur.

For potable water projects, the material name alone is not enough. The exact valve, coating and wetted components should comply with the required approval, such as WRAS, ACS, WaterMark or NSF/ANSI/CAN 61 depending on the market. NSF explains that NSF/ANSI/CAN 61 covers drinking water system components including valves, joining and sealing materials, pipes and non-metallic potable water materials.

Related reading: Choosing Potable Water Butterfly Valves (WRAS, ACS, WaterMark).

When should you choose NBR butterfly valve seats?

Choose NBR, also called nitrile or Buna-N, when oil resistance is more important than water aging or outdoor ozone resistance. NBR is commonly used for petroleum oils, lubricants, hydraulic fluids and some gas applications.

Compared with EPDM, NBR has better resistance to oils and fuels, but it is usually weaker in ozone, sunlight, hot water and steam service. In practice, NBR should not be selected just because it is available or inexpensive. It should be selected because the medium is oil-based and the temperature is within the compound's rated range.

If the project is municipal water, potable water, chilled water or outdoor HVAC, EPDM is normally a safer starting point than NBR. If the project is an oil line, fuel line or compressor-related service, NBR may be the more logical first choice.

When should you choose PTFE butterfly valve seats?

Choose PTFE when chemical resistance is the main risk. PTFE is not a rubber; it is a fluoropolymer with very low friction and strong chemical inertness. In butterfly valves, PTFE is often used as a seat, liner or full lining to isolate corrosive media from the metal valve body.

PTFE is a strong option for many acids, alkalis, solvents and aggressive chemical fluids. It is also useful when media purity matters because it has low adhesion and low contamination risk. But PTFE is less elastic than rubber, so the valve design must control compression, torque and long-term creep. A poorly designed PTFE seat can leak even when the material is chemically compatible.

Use PTFE carefully in slurry or fluids with hard particles. Abrasive solids can damage the lining or sealing surface. For these services, a different seat design, harder material or metal-seated valve may be required.

For detailed product selection, see What Is a PTFE Lined Butterfly Valve and How to Select It.

When should you choose Viton or FKM butterfly valve seats?

Viton is a well-known trade name for FKM fluoroelastomer. Choose FKM when the seat needs better heat, oil, fuel and chemical resistance than standard EPDM or NBR can provide. It is often selected for higher-temperature industrial service, chemical media and oil-related systems.

FKM is not automatically better for every valve. It is more expensive, and it does not have the same low-temperature flexibility as EPDM or NBR. It can also be unsuitable for some media, such as certain amines, hot water/steam conditions or strong bases depending on the exact formulation. Always check the actual FKM compound against the media concentration and temperature.

Use FKM when the project needs a balanced rubber seat with stronger chemical and temperature resistance, but does not justify a PTFE lined valve or a metal-seated design. For standard water service, EPDM is normally more cost-effective.

When should you choose a metal-seated butterfly valve?

Choose a metal seat when soft seats cannot survive the service condition. Metal-seated butterfly valves are used for higher temperature, abrasive particles, high pressure, steam, severe chemical service or applications where fire-safe or tight shutoff requirements drive the design.

Metal seats are not only about the material. The structure matters. Double-offset and triple-offset butterfly valves reduce friction between the disc and seat, which improves durability and makes higher-performance sealing possible. A concentric rubber-seated valve and a triple-offset metal-seated valve are not interchangeable, even if the nominal size and flange drilling look similar.

For a detailed comparison, read Soft-Seated vs Metal-Seated Butterfly Valves: Differences and Selection Guide.

How do media, temperature and pressure change seat selection?

Media compatibility should be checked first, then temperature, then pressure and cycling conditions. A seat material can look correct on paper but still fail if the valve is operated near its temperature limit, exposed to frequent cycling, installed with flange misalignment or used in a fluid with unexpected additives.

Media type

Water-based systems usually start with EPDM. Oil-based systems usually start with NBR or FKM. Corrosive chemical systems often start with PTFE or FKM. Abrasive slurry or high-temperature service may require metal seats or special valve designs.

Temperature

Temperature affects hardness, elasticity, creep and sealing force. Rubber seats can harden, soften or swell outside their rating. PTFE can creep under load. Metal seats tolerate higher temperature but often require more precise machining and higher torque.

Pressure and shutoff

Soft seats usually provide excellent shutoff in low-to-medium pressure systems. Higher pressure, frequent pressure shock or severe differential pressure may require a high-performance butterfly valve design. API 609 notes that some butterfly valve categories can have seat ratings different from body ratings, so never assume body pressure rating equals seat pressure rating.

How should buyers specify butterfly valve seat material in an RFQ?

A good RFQ should describe the service condition instead of only naming a seat material. This helps the manufacturer confirm compatibility and avoid a mismatch.

• Medium name, concentration, additives and whether solids are present
• Operating temperature and maximum temperature
• Operating pressure, differential pressure and pressure shock risk
• Valve size, connection type and flange standard
• Required shutoff class or test standard
• Actuation method and cycling frequency
• Required approvals such as WRAS, ACS, WaterMark, NSF/ANSI/CAN 61, API 609 or EN 593
• Whether the seat should be replaceable, bonded, vulcanized or fully lined

If you already know the exact material, write it clearly: EPDM, NBR, PTFE, FKM/Viton or metal seat. If you are unsure, send the operating data and ask for a material recommendation with a compatibility explanation.

Practical selection guide by application

Common mistakes when selecting butterfly valve seat materials

• Choosing by temperature only. A material may handle the temperature but fail chemically.
• Using EPDM in oil service. EPDM is strong in water service but usually poor with hydrocarbons.
• Using NBR for potable water without approval. Potable water requires approved wetted materials, not just a familiar rubber name.
• Assuming PTFE means zero risk. PTFE has excellent chemical resistance, but design, creep, abrasion and torque still matter.
• Ignoring seat pressure rating. Seat rating can differ from body rating, especially in high-performance butterfly valves.
• Not planning maintenance. If the system requires easy service, ask whether the seat is replaceable before ordering.

For maintenance planning, see How to Replace a Butterfly Valve Seat.

Frequently asked questions

Is EPDM or PTFE better for butterfly valve seats?

Neither is universally better. EPDM is usually better for water, HVAC and municipal systems because it is elastic and cost-effective. PTFE is usually better for corrosive chemicals because it is more chemically inert. The correct choice depends on media, temperature, pressure and certification requirements.

Can NBR be used for water butterfly valves?

NBR can seal some water systems, but it is usually chosen for oil-based media rather than long-term water service. For municipal water, chilled water or potable water, EPDM is normally a better starting point, provided the exact compound has the required approval.

Is Viton the same as FKM?

Viton is a trade name for a type of FKM fluoroelastomer. In valve specifications, FKM is the generic material family, while Viton refers to branded fluoroelastomer compounds. Always confirm the exact compound, because chemical compatibility can vary by formulation.

When should I use a metal seat instead of a soft seat?

Use a metal seat when temperature, abrasion, pressure, fire-safe requirements or severe service conditions exceed the safe range of rubber or PTFE seats. Metal-seated butterfly valves often use double-offset or triple-offset designs to reduce wear and improve sealing performance.

What information should I send to select the right seat material?

Send the medium name and concentration, temperature, pressure, solids content, valve size, connection standard, cycling frequency, shutoff requirement and any required approvals. With these details, a manufacturer can recommend EPDM, NBR, PTFE, FKM or metal seat more accurately.

Conclusion: choose the seat material around the service condition

Butterfly valve seat material selection should start with the service condition, not with a habit or a price target. EPDM is usually the practical choice for water. NBR belongs mainly in oil service. PTFE is strong for corrosive chemical media. Viton/FKM fits higher-temperature and more demanding fluids. Metal seats are reserved for severe service where soft materials cannot survive.

If you are comparing seat materials for a current project, Union Valve can review your medium, temperature, pressure, connection standard and certification requirements before recommending a valve configuration. You can also browse our butterfly valve range or contact us with your working conditions.

Sources and further reading

• API Standard 609: Butterfly Valves, Double-flanged, Lug- and Wafer-type.
• NSF/ANSI/CAN 61: Drinking Water System Components - Health Effects.
• Parker O-Ring Handbook ORD 5700.
• EPDM vs PTFE Butterfly Valve Seats: Selection Guide.
• Butterfly Valve Seat Types, Materials, and Selection Guide.

About the Author

Serena Zhang

Sales Manager · Tianjin Union Valve Co., Ltd

With 4 years of valve export experience and dedicated service, Serena ensures a smooth and reliable order process. Quick replies 24/7. Welcome your inquiries!