Is Viton™ the same as FKM?

No. Viton™ is a type of FKM fluoroelastomer, but not all FKM materials are Viton™. Viton™ is a branded material family produced under Chemours™ standards, while other manufacturers also produce FKM materials.

What is the difference between FKM and fluorosilicone?

FKM fluoroelastomers are fluorinated carbon-based materials with strong resistance to aggressive chemicals and high temperatures. Fluorosilicones are silicone-based materials with fluorocarbon characteristics and are often preferred when low-temperature flexibility is especially important.

What are the advantages of Viton™ and FKM materials?

Viton™ and FKM materials provide excellent resistance to oils, fuels, hydraulic fluids, lubricants, acids, alkalis, and many solvents. They also offer high-temperature resistance up to about 400°F, low gas permeability, strong tensile properties, and good resistance to ozone, UV exposure, and weathering.

What are the disadvantages of Viton™ and FKM materials?

Compared with common elastomers such as nitrile or EPDM, Viton™ and many FKM materials are more expensive. Many grades also stiffen at temperatures below about 30°F, which can reduce flexibility and sealing performance in cold environments.

Material

Fluoroelastomer (FKM)

Fluoroelastomers are used for applications that require excellent resistance to aggressive chemicals

Stockwell Elastomerics uses various fluoroelastomer (FKM) materials, including Viton™, to make gaskets for aerospace, analytical instrumentation, chemical processing, and other demanding applications with exposure to high heat and aggressive chemicals. Using manufacturing processes such as molding, die cutting, and waterjet cutting, Stockwell Elastomerics fabricates custom FKM gaskets and seals at its manufacturing facility in Philadelphia, Pennsylvania.

What is a Fluoroelastomer?

Fluoroelastomers are a family of high performance elastomers that are often referred to as FKM. A fluoroelastomer is a type of synthetic rubber that contains fluorine in its polymer structure. FKM material was originally developed by DuPont™ as Viton™ in 1957. After DuPont™ spun off Chemours™ in 2015, the trademark rights to Viton™ were transferred to The Chemours Company FC, LLC.

The distinguishing characteristics of FKM in general and Viton™ and particular are their resistance to high temperatures up to 400°F (200°C) and the high resistance to a broad range of aggressive chemicals, including fuels, oils, acids, and solvents. These synthetic rubber materials also offers excellent resistance to ozone, ultraviolet (UV) light, and weathering.

Like other types of mechanical seals, Viton™ and fluoroelastomer materials help prevent leaks between two joined or mating surfaces. Fluoroelastomer gaskets compensate for minor surface irregularities and ensure a consistent, reliable seal under harsh conditions. In addition to filling gaps, fluoroelastomer gaskets protect against heat transfer and maintain a seal with thermal expansion or contraction. Compared to fluorosilicones, gaskets made with fluoroelastomers / Viton™ offer advantages for applications where a specific set of aggressive chemicals are present.

Why is Fluoroelastomer called FKM?

F is for Fluorine (fluorine is present in the polymer backbone)
K is from the sequential designation in ASTM standards, not from a letter in the name
M is based on ASTM’s classification of rubber structures, where the “M” refers to a saturated carbon chain that exists in fluoroelastomers and silicones

Fluoroelastomers vs. Fluorosilicone

Fluoroelastomers and Viton™ are not the same as fluorosilicone. That’s because Viton™ is a type of fluoroelastomer (FKM), a category of fluorocarbon-based materials that includes perfluoroelastomers (also called FFKM). Fluorosilicones (FVMQ) have fluorocarbon characteristics but are based on silicone rubber with fluorine additions in the main polymer chain.

Fluoroelastomers and fluorosilicones both provide chemical and temperature resistance, but they have different chemical compositions and performance properties. The table below explains.

Property	Viton™ (FKM)	Fluorosilicone (FVMQ)
Chemical Composition	Made from fluorinated carbon-based polymers.	Combines silicone and fluorocarbon properties
Temperature Resistance	High temperature resistance up to 400°F (200°C) or more.	Excellent temperature resistance, at ~450°F/232°C.
Chemical Resistance	Superior resistance to oils, fuels, and many aggressive chemicals	Good resistance to fuels, oils, and solvents, but less resistant to some chemicals than fluoroelastomer
Low Temperature Flexibility	Stiffens at lower temperatures. Not recommended for low temperature applications.	Retains flexibility at very low temperatures, some compounds down to -80°F

In summary, Viton™ is better for aggressive chemicals while fluorosilicone excels at low temperature flexibility while offering good chemical resistance.

Viton™ vs. FKM and FFKM

All Viton™ materials are FKM (fluoroelastomer) materials, but not all FKM material is Viton™. Although Viton™ is one of the most widely used types of FKM, manufacturers such as 3M™, Solvay™, and Daikin™ have their own FKM products. Viton™ is produced under the strict manufacturing standards of Chemours™ and is generally more expensive than other FKM materials because of its branding, quality assurance, and multiple grades.

Viton™ is not a perfluoroelastomer (also called FFKM), but FFKM material may be required for applications in the semiconductor and pharmaceutical industries. That’s because FFKM materials such as Kalrez® (a DuPont™ product) have low outgassing and high purity properties. FFKM is more expensive, however, and this can make Viton™ a better choice for applications that don’t require the extreme performance of FFKM.

Another material to consider is AFLAS®, a distinct type of fluoroelastomer, a tetrafluoroethylene-propylene (FEPM) copolymer, made from tetrafluoroethylene and propylene (TFE/P), developed by AGC Chemicals.

Grades of Fluoroelastomers for Gaskets

Fluoroelastomers, like other polymers, are available in different grades with specific benefits for different sealing applications. Contact Stockwell Elastomerics’ Applications Engineers for gasket material selection assistance.

Advantages of Viton™ and FKM materials

Viton™ and FKM materials resist a wide range of aggressive chemicals, including:

Oils, fuels, and petroleum-based fluids
Hydraulic fluids and lubricants
Acids, alkalis, and organic solvents

This makes Viton™ / FKM especially effective in environments where other elastomers, such as nitrile or EPDM, would degrade. In addition to high temperature resistance, Viton™ / FKM materials have low gas permeability, which makes them a good choice for fuel systems and vacuum applications. Viton™ and FKM perform well with a broad range of fluids, including biodiesel and oxygenated fuels.

Among their advantages, fluoroelastomer materials have exceptional tensile strength (upwards of 2000psi) and are tear and abrasion resistant. Viton™ is also inherently flame-resistant and self-extinguishing once the heat source is removed. Specific grades or types include general purpose (Viton™ A), enhanced chemical resistance (Viton™ F), and specialty grades that are FDA-compliant or designed for extreme high performance.

Disadvantages of Viton™ / FKM

Viton™ is more expensive than common organic elastomers such as nitrile or EPDM. Most Viton™ grades stiffen at temperatures below 30°F (-15°C) resulting in a loss of flexibility and sealing capabilities. For cold environments like this, gaskets made of silicones or fluorosilicones may be a better choice.

Among their disadvantages, Viton™ materials are relatively dense, which can limit their utility in lightweight applications. Compared to other elastomers, including natural rubber and nitrile, Viton™ also has less elasticity. This makes it less than ideal for sealing and cushioning applications that require high stretch or recovery.

Viton™ resists most chemicals, but they’re less effective against the following substances.

Ketones and amines
Hot water and steam over prolonged periods
Organic acids in high concentrations

FFKM may be a better choice for these applications, and certain grades of Viton™ may degrade more quickly in high radiation environments such as nuclear applications.

Frequently Asked Questions about Fluoroelastomers

What are fluoroelastomers (FKMs)?

Fluoroelastomers (FKMs) are high‑performance fluorinated polymers that resist high heat, oils, fuels, hydraulic fluids, lubricants, acids, alkalis, and organic solvents. Viton™ (Chemours) is the best‑known brand name, but other manufacturers also produce their own brands of FKM materials. FKM is the generic ASTM D1418 designation for fluoroelastomers.

How does Viton™ compare to other FKMs?

All Viton™ materials are FKMs, but not all FKMs are Viton™. Viton™ is produced under Chemours’ strict quality standards and is optimized for improved sealing effectiveness, especially where flexibility and resilience are critical. Non-Viton™ FKMs can vary widely in fluorine content, curing methods, and formulation. As a result, these materials have different properties than Viton™.

What are the main advantages of FKM materials over other elastomers?

FKM materials combine excellent chemical and high-temperature resistance (400°F) with a tensile strength that typically exceeds ~2000 psi. They also have low gas permeability and combine flame resistance with self-extinguishing behavior. Compared to organic elastomers like nitrile and EPDM, FKM provides better performance in harsh environments.

What are the limitations of fluoroelastomers?

FKM materials are more expensive than commodity elastomers. They also stiffen at low temperatures (some below ~30°F) and have lower elasticity in general. Compared to silicone, FKM is less effective against hot water/steam, and high‑concentration organic acids. FKM’s strength is its resistance to hydrocarbons and solvents – not polar fluids. FKM withstands oils, certain fuels, and petroleum-based fluids that EPDM and silicone typically cannot.

Does FKM come in grades?

Yes. FKM comes in three major grades. Each is designated with a letter.

Type A: General Purpose
Type B: Improved Chemical Resistance
Type F: High Fluorine, Harsh Chemical Grade

There are also specialty FKM grades for niche requirements. Examples include low-temperature, FDA-compliant, low compression set, and peroxide-cured FKM.

Which fluoroelastomers does Stockwell Elastomerics offer?

Stockwell Elastomerics offers Type A Viton® materials that are soft (55 durometer), firm (65 durometer), or extra firm (75 durometer). These fluoroelastomers have a temperature range of -32°C to 204°C (-25.6°F to 400°F) and offer excellent compression set resistance. They are recommended for general-purpose sealing and with aerospace fuels and lubricants.

Does Stockwell Elastomerics use genuine Viton™?

Yes. Stockwell Elastomerics uses genuine Viton™. It’s made by Eagle Elastomer, Inc., a compounder that sources its base material directly from Chemours. Because Chemours grants Eagle Elastomer a formal license to use the Viton™ brand name, the compounder must use 100% pure Chemours base fluoroelastomers in its materials. This makes it genuine Viton™ instead of generic Viton®.

Which industries commonly use FKM materials?

FKM materials are commonly used in harsh environments where exposure to aggressive fluids and elevated temperatures is routine. Examples include aerospace and defense, analytical instrumentation, chemical processing, semiconductors and electronics, and HVAC and refrigeration.

What’s the difference between FKM and FFKM?

FKM is a partially fluorinated polymer (fluoroelastomer) that contains hydrogen atoms in its backbone. FFKM is a fully fluorinated polymer (perfluoroelastomer) that does not. Practically speaking, the absence of hydrogen atoms in FFKM’s backbone dramatically increases its chemical and thermal stability.

When should engineers consider FKM instead of FFKM?

For semiconductor, pharmaceutical, or ultra‑high‑purity applications, FFKM may be required due to its extreme chemical resistance and low outgassing. Because of this extreme chemical resistance, FFKM is denser and sacrifices flexibility. FKM is therefore a better fit in applications where a material must maintain flexibility throughout thermal cycles. FFKM is significantly more expensive than FKM. This makes FKM a better choice for most industrial and aerospace applications that require resistance to high heat and chemicals, but which are not integral to propulsion systems.

Contact Stockwell Elastomerics for Fluoroelastomers and Viton™ Gasket Materials

Contact us for gaskets made with Viton™ and other fluoroelastomer materials, and for assistance with material selection. If Viton™ / fluoroelastomer material is not the best choice for a specific application, Stockwell Elastomerics’ Applications Engineers can recommend other material options.

Viton™ is a registered trademark of The Chemours Company FC, LLC.
Chemours™ is a registered trademark of The Chemours Company FC, LLC.
DuPont™ is a registered trademark of DuPont de Nemours, Inc.
3M™ is a registered trademark of 3M Company.
Solvay™ is a registered trademark of Solvay SA.
Daikin™ is a registered trademark of Daikin Industries, Ltd.
AFLAS® is a registered trademark of AGC Chemicals.