Buna-N and FKM, both belong to the best class of elastomers. However, there is a recent trend towards users preferring FKM especially in automotive industry. FKM possess superiority over Buna-N in heat tolerance, permeation, compression as well as defence against biofuels, particularly ethanol. However, Buna-N O-Rings are preferred in hydraulic/pneumatic motors, cylinder, pumps, and valves.

Both Buna-N and FKM have poor resistance to Esther, Ketones, Amine and Brake fluid, ButFKM has superior resistance to Halogenated solvents when compared to Buna-N. FKM is also excellent in situations requiring higher heat tolerance and resistance to a broader range of chemicals.

Given below is the detailed description of Buna-N and FKM characteristics.


Buna- n is also known as NBR (acrylonitrile butadiene rubber) or nitrile. It is the most commonly used elastomer for O-Rings and other seals. It is the synthetic rubber copolymer of ACN (acrylonitrile) and butadiene.

  • Temperature range

Temperature ranges from -40°C to 140°C

  • Features
  • It imparts elasticity and low temperature flexibility.
  • Nitrile has very good aging properties under severe conditions.
  • Nitrile compound has high tensile strength that outperform other elastomers.
  • It has an excellent abrasion, tear and compression set resistance.
  • It has poor resistance to ozone, sunlight and weathering as the double bond is present in the polybutadiene segment of the chemical back bone, hence seal from nitrile bases should not be stored near electric motors or ozone generating equipments.


  • Cold water
  • General purpose sealing
  • Petroleum oil and fluids
  • Silicone oils and grease
  • Water( below 2120C)
  • Ethylene glycol base fluids( hydrolubes)


  • Strong acid
  • Automotive brake fluids
  • Aromatic hydrocarbons(benzene, xylene)
  • Ketones
  • Nitro hydrocarbons
  • Halogenated hydrocarbon


It is used in engines, gearboxes and also can be found in anything from shower heads, garden hoses, and pumps up to an aircraft. Nitrile O-Rings are used as a face to face gasket style seal or as a shaft seal, and allow both rotary and linear movement.



FKM(Viton) or Fluoropolymer. FKMelastomer was introduced in mid 1950s and since then have become of major importance in the seal industry.

  • Temperature range

Temperature ranges from -32°C to 232°C

  • Features
  • FKM has excellent chemical and high temperature resistance and retains its mechanical properties better than most elastomer at elevated temperatures.
  • Exceptional good resistance to oxidation, ozone, sun and weather.
  • Good electrical properties in low voltage, low frequency application.
  • Gas permeability and compression set is low


  • Silicone fluids
  • Halogenated Hydrocarbons
  • Acids
  • Selected phosphate ester fluids
  • Diester lubricants
  • Solvents
  • Vacuum applications
  • Petroleum products


  •  Skydrol fluids
  •  Steam and water( above 1000C)
  •  Hot Hydrofluoric or Chlorosulfonic
  •  Low molecular Ester and Esther
  •  Amines and Ammonia
  •  Ketones


FKM O-Rings are considered for seal use in aircraft, oil and gas, automobile, scientific instruments and other mechanical devices requiring maximum resistance to elevated temperature, and to many functional fluids. They are widely used in diffusion pumps on vacuum systems and on vacuum flanges on mass spectrometers and electron microscopes.