FKM vs Viton vs FPM: Same Fluoroelastomer, Different Names

FKM, FPM and Viton refer to the same family of fluorocarbon elastomers (fluoroelastomers). The difference is naming, not chemistry: FKM is the ASTM D1418 designation, FPM is the ISO 1629 / DIN designation, and Viton is the Chemours (formerly DuPont) trade name. In short: all Viton is FKM, but not all FKM is Viton.

Quick answer: FKM, FPM and Viton all mean fluoroelastomer — the same fluorine-containing rubber family with 66–70% fluorine and a −20°C to +200°C continuous service range. FKM is the ASTM name, FPM is the ISO/DIN name, and Viton is Chemours' brand for a specific family of FKM grades. When a drawing says "Viton" or a specification says "FKM," they request the same material class; confirm the specific grade and hardness to avoid substitution errors.

The Three Names

Name	Origin	Meaning
FKM	ASTM D1418 (US)	Generic designation for fluorocarbon (fluoroelastomer) rubber
FPM	ISO 1629 / DIN (EU)	The same fluorocarbon rubber under the ISO/DIN naming scheme
Viton	Chemours (formerly DuPont)	Trade name for a specific family of FKM grades

FKM and FPM are the ASTM and ISO/DIN designations for the same material class; Viton is one brand of FKM. None of the three is a chemical formula — they are naming conventions for fluorocarbon rubber.

When Does the Naming Matter?

For procurement, the naming matters in three situations:

Drawings vs specifications — a drawing that says "Viton" and a specification that says "FKM" request the same material class. Request the specific grade (A, B, GF, GFLT) and hardness to avoid ambiguity.
Equivalent brands — Viton is one FKM brand; other suppliers make FKM under different names. An "FKM" callout without a brand name is a generic request that any qualifying FKM compound can fill.
Substitution risk — because "Viton" is a premium brand name, some suppliers mark generic FKM (or non-FKM) as "Viton-equivalent." Request material test reports and confirm fluorine content to verify.

Viton / FKM Grade Mapping

Viton Grade	FKM Type	Typical Use
Viton A	FKM Type 1 (66% F, dipolymer)	General oil and chemical resistance
Viton B	FKM Type 2 (68% F, terpolymer)	Improved fuel resistance
Viton GF	FKM (cure-site monomer)	Base/amine resistance
Viton GFLT	FKM low-temperature	−40°C fuel service

Grade and fluorine data follow O-Ring Supply Co. material specifications — see the NBR vs FKM (Viton vs Buna-N) comparison for the full property tables.

FKM vs FFKM: A Separate Distinction

Do not confuse FKM (fluoroelastomer, 66–70% fluorine) with FFKM (perfluoroelastomer, fully fluorinated). FFKM offers near-PTFE chemical resistance and higher temperature capability but costs far more — Kalrez and Chemraz are FFKM brands. See FKM vs FFKM for the full comparison.

Frequently Asked Questions

Q1: Is Viton the same as FKM?

Yes. Viton is Chemours' trade name for a family of FKM fluoroelastomer grades. Every Viton O-ring is FKM; not every FKM is branded Viton.

Q2: What is the difference between FKM and FPM?

They are the same material under different naming schemes — FKM is the ASTM D1418 designation, FPM is the ISO 1629 / DIN designation.

Q3: What does FKM stand for?

FKM is the ASTM D1418 designation for fluorocarbon (fluoroelastomer) rubber. It is a material-class designation, not a chemical formula.

Q4: Is FFKM the same as FKM?

No. FFKM is perfluoroelastomer — fully fluorinated, with higher temperature and chemical resistance and a much higher cost. FKM is standard fluoroelastomer.

Q5: Should I specify "Viton" or "FKM" on a purchase order?

Either is acceptable for the material class. Specify the grade (A, B, GF, GFLT), hardness (Shore A), and size standard (AS568/ISO 3601) to get the correct compound. For critical chemical service, request fluorine content and a material test report.

---

Need FKM (Viton) O-rings? Request a quote with your grade, hardness, size and fluid, or contact us for compound selection. We supply standard FKM (Viton A/B equivalents), low-temperature GLT grades, and FFKM for demanding service.