Gaskets and Seals: FKM vs. FFKM

Following on from our recent blog on fluoroelastomer gaskets and seals for severe operating conditions, a question we are sometimes asked is, what is the difference between fluoroelastomer (FKM) and perfluoroelastomer (FFKM) materials? In this blog, we take a look at the differences between these two sealing materials, as well as the applications which they are appropriate for servicing.

What is FKM?

Fluoroelastomer is the ASTM designation for a high-performance fluorinated synthetic rubber. FKM rubber has excellent resistance to heat and chemicals. Gaskets and seals made from FKM material have outstanding resistance to oxygen, ozone, UV and heat (up to 200°C), as well as swelling by oils, aromatic and chlorinated hydrocarbons, and fuels.

FKM materials are used to manufacture gaskets, seals and O-rings for severe service conditions found in automotive, aerospace, energy, and other industrial applications. Viton® is perhaps the most widely known example of a fluoroelastomer and is a registered trademark of The Chemours Company (formerly DuPont).

What is FFKM?

Perfluoroelastomer is a synthetic rubber that contains higher amounts of fluorine than standard FKM - the prefix "per" signifies that the compound is fully fluorinated. This higher fluorine concentration gives FFKM even greater high temperature and chemical resistance than FKM. With its superior temperature resistance and nearly universal chemical compatibility, gaskets and seals produced from FFKM are often selected for critical applications where seal failure can result in serious harm to personnel or the creation of an extremely hazardous condition.

FFKM material has properties and performance characteristics similar to PTFE (polytetrafluoroethylene). FFKM gaskets and seals can withstand the harshest conditions, including environments such as those found in semiconductor manufacturing where oxygen plasma is present.

FFKM material is often used to make gaskets, seals and O-rings that involve contact with highly corrosive fluids or hydrocarbons, as well as applications with maximum continuous service temperatures up to 327°C. These gaskets and seals also provide low outgassing in vacuum-sealing applications. Applications which are suitable for the use of FFKM gaskets and seals are often found in the aerospace, energy, pharmaceutical, semiconductor, and process industries.

Kalrez®, a registered trademark of The Chemours Company, is an example of a perfluoroelastomer.

When should you choose gaskets and seals made from FFKM material?

Using gaskets and seals produced from FFKM can mean lower operating costs resulting from less frequent seal changes and repairs. If you have a demanding application involving the use of high temperatures and aggressive media, FFKM gaskets and seals can provide significant cost and revenue benefits.

The proven reliability of FFKM seals in demanding applications also lessens the need for frequent inspections of seal integrity. The net result – lower costs from less maintenance. At the same time, process throughput, productivity and yields are enhanced from increased equipment uptime.

In semiconductor manufacturing, FFKM gaskets and seals can also help prevent process contamination by reducing particulate matter while decreasing extractables and withstanding degradation in harsh plasma environments. FDA-compliant FFKM materials are also available for producing gaskets and seals which can service applications in the food, beverage, and pharmaceutical industries.

FKM and FFKM gaskets and seals from CRG

If you have a severe service or critical application which requires the use of FKM or FFKM gaskets and seals, CRG can help! Using our advanced converting capabilities, CRG can fabricate a wide range of gaskets, seals, and parts from FKM or FFKM materials. These products are made using the latest CNC fabrication technology in our ISO 9001:2015 certified facility. Our experienced team will recommend the appropriate material, and produce the finished parts to your exact specifications.

To find out more about CRG FKM and FFKM gaskets and seals, please contact our sales team at