Comparison of The Different Grades of FKM Polymers


Not all FKM rubber compounds are the same. People in the industry often refer to all FKM or fluoroelastomer rubbers as Viton®. Viton® is a trade name for the polymer once owned by Dupont™ that is now sold by Chemours™. There are a few different suppliers of FKM polymers, but they use other trade names for the polymer. 

FKM Rubber Formulation

FKM rubber formulations typically have polymer, filler, activator, processing aid, and curatives. These formulations are more simplified than EPDM or NBR compounds. Due to the material’s high performance, the polymer gives the most physical and chemical characteristics, so ingredient loading is less. High-end compounds won’t have plasticizers that extract or burn off at high temperatures. As with most formulations, it is a parts per 100 (PHR) polymer. 

Ingredient           PHR

Polymer                  100

Acid Acceptor        0 –  6

  Fillers                    5 – 60 

Processing Aids    0 – 2

Cure System          1 – 8

Polymer:  Dipolymer, Terpolymer or special.  

Acid Acceptors: Magnesium Oxide, Calcium Hydroxide, Zinc Oxide

Fillers: Carbon Black, Clay, Barium Sulfate

Processing Aids: Paraffin Wax, Fatty Acids, Silicone

Cure System: Bisphenol, Peroxide, Co-agents

Polymer Types

Chemours Viton® uses three different designations: A, B, or F type polymers. The difference is in the polymer’s fluorine levels, which relates to its resistance to attack by fluids or chemicals. The two methods of curing are bisphenol and peroxide. An identifying difference between these polymers is the volume swell in methanol or low molecular weight oxygenated solvents. For example, if an FKM rubber is immersed in methanol for 168 hrs at 23°C, you can expect to have swells close to 90% for A, 40 % for B, and 5% for F.  This is an excellent test for determining what type of polymer is being used. 

A type or ASTM D1418 FKM Type 1: Dipolymer of hexafluoropropylene (HFP) and Vinylidene Fluoride (VF2).

B and F Type or ASTM D1418 FKM Type 2: Terpolymer of HFP and VF2 with Tetrafluoroethylene (TFE).

ASTM D1418 FKM Type 3 – Low Temperature FKM uses a fluorinated vinyl ether monomer. Depending on the polymer can be similar chemical resistance as A or F type. 

ASTM D1418 FKM Type 5is a tetra polymer of ethylene, tetrafluoroethylene (TFE) and perfluoromethyl vinyl ether (PMVE). This combination gives outstanding chemical resistance.

Polymer Producers

Chemours – Viton

Daikin Chemical – Dia-El

3M Dyneon – Dyneon *Will discontinue production in 2025

Solvay Speciality Polymers – Tecnoflon

Chemical Resistance

                            Polymer Type 
Application Contact: A B F GF GLT GFLT ETP
Cure System Bisphenol Peroxide
Aliphatic  Hydrocarbons  1 1 1 1 1 1 1
Aromatic Hydrocarbons 2 1 1 1 2 1 1
Automotive fuels (NO Alcohol) 1 1 1 1 1 1 1
Automotive Fuels (5 to 15% Alcohol) 2 1 1 1 2 1 1
Automotive Fuels (up to 100% Alcohol) NR 2 1 1 NR 1 1
Engine Lubricating Oils (SE-SF grades) 2 1 1 1 1 1 1
Engine Lubricating Oils (SG-SH grades) 3 2 2 1 1 1 1
Acid, Hot Water, Steam 3 2 2 1 1 1 1
Strong Base, High PH, Amines NR NR NR NR NR NR 2
Low Molecular Weight Carbonyls – (MTBE, MEK, MIBK) NR NR NR NR NR NR 2
Low Temperature Flexibility (TR-10) ‘C -17 -14 -7 -6 -30 -24 -11

1 – Little to Minor Effect, 2 – Minor To Moderate Effect, 3 – Moderate to Severe Effect , NR- Not Recommended


Industrial Uses

  • O-rings
  • Vacuum seals
  • Heat and corrosion resistant expansion joints
  • Packing rings for hydraulics
  • High precision molded balls for check valves
  • Chemical resistant grommets
  • Automotive seals for flex fuels


  • O-rings
  • Exhaust Housing Seals
  • Low Outgassing Seals

Fluid Power

  • Hydraulic seal – U-cups, V-packing rings
  • Pump Seals


  • Low friction pump seals
  • Non-leaching chemical seals
  • Sanitary Gaskets

Apple Rubber molds many different polymer types for various applications and industries. We recommend asking us which polymer is correct for your application. Not all FKM compounds are the same. Changing polymer type and cure systems can make your part go from failure to success. FKM compounds can be used up to 300°C for a short period of time and down to -54°C for some static applications.