FKM vs. ffkm

FKM and FFKM share many similarities. Understanding the differences is critical in helping determine the appropriate sealing solution for your application.

What is fkm?

FKM is the ASTM designation for a class of fluorinated, carbon-based synthetic rubber, commonly known as fluoroelastomer. FKM has impressive heat resistance, allowing FKM seals to withstand temperatures greater than 200°C. FKM also exhibits extraordinary levels of resistance to high pressures, chemicals and other fluids (including several fuels).

FKM was originally developed in the late 1950s in response to demand for high performance seals in the aerospace industry. Development of FKMs continued through the 1980s, with advancements including greater thermal stability and improved heat, solvent, and compression resistance.

Today, FKM materials are commonly used to manufacture o-rings, seals, and gaskets for a variety of high-performance applications in the automotive, aerospace, energy, semiconductor, and industrial industries.

what is ffkm?

FFKM, or perfluoroelastomer, contains higher amounts of fluorine than standard FKM, and features higher temperature ratings, up to approximately 325°C. FFKM also has improved chemical resistance, with nearly universal chemical compatibility. This combination of high-performance capabilities makes FFKM seals the premium choice for the most challenging applications.

The first commercially available FFKM seal was produced in the late 1960s. However, widespread manufacturing of FFKM materials did not occur until the late 1980s due to patent restrictions.

FFKM is used in o-rings and seals in environments with high temperatures and/or harsh chemicals in the aerospace, semiconductor, energy, pharmaceutical and industrial industries.

FKM vs. FFKM Comparison

See a comparison chart for other material compounds here.

FKM and FFKM Solutions by Greene, Tweed

Greene, Tweed offers a broad range of FKM and FFKM sealing solutions to meet the specific demands of the industries and applications we serve.

Greene, Tweed’s proprietary FFKM material, Chemraz®, has the broadest chemical resistance of any elastomeric material, combining the resilience and sealing force of an elastomer with chemical resistance approaching that of PTFE.

Chemraz® Perfluoroelastomers (FFKM)

Fluoroelastomers (FKM)

FKM Versus FFKM – A Comparison of Properties

Estimated temperature range (°C/°F)-20 - 250 (-4 to 482)-40 - 325 (-40 to 617)
Heat resistance (ASTM D2000) (°C/°F)225/437 (Type G)250/462 (Type H)
Elongation @ break, % (ranges)70 – 300100 – 300
Compression set15-25% (on 214 o-ring after 70 hr @ 200°C)15-25% (on o-ring after 70 hr @ 200°C); better at higher temperatures: 15-30% (on o-ring after 70 hr @ 300°C)
Hardness range (Shore A)60 to 9565 to 95
Tensile strength range (psi/MPa)1,500/1.03 to 4,500/3.101,250/8.61 to 3,600/24.8
Specific gravity1.8 to 2.01.9 to 2.2
Fluorine content of polymer (%)66 - 70%71 - 73%
Chemical resistanceBroad range of chemicals: ga-soline, alcohol, fuel additives, acids, hydrocarbons, water, oils, oxidation, ozone, radiationBroadest range of chemical resistance
Industry applications
  • Aerospace
  • Automotive
  • Energy
  • Industrial
  • Semiconductor
  • Aerospace
  • Energy
  • Industrial
  • Pharmaceutical
  • Semiconductor (dominant market)
  • Good wear resistance
  • Excellent compression set
  • Great heat resistance
  • Superior swell resistance in high octane and oxygenated fuels
  • Excellent thermal resistance
  • Excellent plasma resistance
  • Excellent chemical resistance
  • Superior compression set at elevated temperatures
  • Outstanding chemical compatibility
    Not recommended for
    • Ketones (MEK)
    • Amines
    • Low molecular weight esters and ethers
    • Nitro hydrocarbons
    • Hot hydrofluoric or chlorosulfonic acids
      • Molten metals
      • Gaseous alkali metals
      • Halogenated freons/fluids
      • Uranium hexafluoride

        Note: Characteristic metrics are provided as generally accepted industry ranges. Actual ranges may vary, depending on specific industry applications, such as additives, formulations, curatives used, etc.