FKM vs FPM vs Viton: What’s the Difference? (2026 Guide)

If you’ve ever shopped for high-performance rubber seals, you’ve probably come across the terms FKM, FPM, and Viton — often used as if they’re interchangeable. But are they really the same thing?

The short answer: they refer to the same base material (fluoroelastomer), but they are not identical in practice. Understanding the distinction can save you from costly specification errors.

In this guide, we’ll break down exactly what each term means, where they overlap, and how to choose the right one for your application.

What Is FKM?

FKM is the ASTM D1418 designation for fluoroelastomer rubber. The “F” stands for fluorine, and “KM” denotes a rubber with saturated backbone and copolymer structure.

Key characteristics of FKM:

• Temperature range: -20°C to +200°C (standard grades), with special grades reaching +230°C
• Chemical resistance: Excellent resistance to oils, fuels, acids, and many solvents
• Compression set: Low, making it ideal for long-term sealing
• Hardness range: Typically 50–90 Shore A

FKM is the most commonly used technical term in North America and Asia when specifying fluoroelastomer materials.

What Is FPM?

FPM is the ISO 1629 designation for the same fluoroelastomer material. The letters stand for:

• F = Fluoro (containing fluorine)
• P = Propylene (copolymer component)
• M = Methylene (saturated backbone)

So when a European engineer specifies “FPM O-rings” and an American engineer asks for “FKM O-rings,” they’re asking for the exact same material — just using different naming standards.

What Is Viton?

Viton® is a registered trademark of The Chemours Company (formerly DuPont). It is a specific brand of FKM fluoroelastomer.

Think of it this way: all Viton is FKM, but not all FKM is Viton. This is exactly like the relationship between “Kleenex” and “facial tissue” — Viton is the brand name that has become synonymous with the material category.

Viton comes in several grades, each optimized for different conditions:

FKM vs FPM vs Viton: Quick Comparison

Do These Differences Matter for Your Project?

For most sealing applications, the practical answer is no — they perform identically when the compound formulation is equivalent. Here’s when it matters:

When to Specify Viton by Name

• Your industry requires Chemours-certified material (aerospace, some OEM specifications)
• Your customer explicitly mandates Viton® in their material specification
• You need traceability to a specific compound datasheet

When FKM (Generic) Is Sufficient

• Your specification only requires fluoroelastomer performance per ASTM D2000
• You need a cost-effective solution without brand premium
• Your application uses standard chemical and temperature ranges

When to Use the FPM Designation

• You’re working with European standards (DIN, EN)
• Your engineering documentation follows ISO conventions
• You’re specifying for EU-based procurement

FKM Material Properties Reference

Regardless of which name you use, here are the typical material properties for standard FKM/FPM/Viton:

Common Applications

FKM/FPM/Viton seals are used across industries that demand reliable performance in harsh environments:

• Automotive: Fuel system seals, valve stem seals, crankshaft seals
• Aerospace: O-rings for hydraulic and fuel systems
• Oil & Gas: Downhole seals, wellhead sealing components
• Chemical processing: Gaskets and seals for aggressive media
• Semiconductor: Seals for plasma and chemical vapor deposition equipment

How to Choose the Right FKM Seal for Your Application

1. Define your operating conditions — temperature range, chemical exposure, pressure
2. Check chemical compatibility — FKM resists many fluids but not ketones, esters, or amines
3. Select the right grade — A-type for general use, B/F-type for aggressive fuels, GLT for low temperatures
4. Specify by performance, not just name — Reference ASTM D2000 callouts (e.g., M2HK810 A2-10) for precision
5. Work with a manufacturer who can provide compound data — Certified material datasheets ensure consistency

Conclusion

FKM, FPM, and Viton all refer to fluoroelastomer rubber, but they differ in naming convention and brand specificity. FKM is the ASTM term used in North America, FPM is the ISO equivalent in Europe, and Viton is a premium brand of FKM made by Chemours.

For most B2B sealing applications, specifying FKM with your required ASTM D2000 grade is sufficient — and it avoids the brand premium of Viton while delivering identical performance.

Need custom FKM seals manufactured to your specifications? Anlintech produces FKM/Viton seal rings and gaskets with full material traceability. Contact us for a quote.