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Seal materials

Choosing the Right Seal Material

The compound matters as much as the profile. This guide summarises the materials most often supplied for industrial seals and what to consider when selecting them.

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NBR

Nitrile Butadiene Rubber

Nitrile, Buna-N

The general-purpose seal elastomer for mineral oils, greases and hydraulic fluids.

General characteristics

  • Good resistance to mineral oils, greases and many hydraulic fluids
  • Good mechanical strength and abrasion resistance
  • Limited resistance to ozone, weathering and sunlight
  • Moderate heat resistance compared with speciality elastomers

Typical applications

  • Oil seals for gearboxes, pumps and motors
  • Hydraulic and pneumatic seals
  • O-rings and static seals for general duty

Advantages

  • Widely available in most profiles and sizes
  • Economical for general industrial duty
  • Well-understood performance in mineral-oil service

Important selection considerations

  • Check compatibility with synthetic lubricants, fuels and additives
  • Not usually the first choice for outdoor exposure or ozone-rich environments
  • Consider FKM or HNBR where operating temperature is elevated

Temperature and pressure capability: depending on compound, design and application.

FKM

Fluoroelastomer

Often known by the trade name Viton™

A fluoroelastomer chosen for elevated temperature and for resistance to oils, fuels and many chemicals.

General characteristics

  • Very good resistance to heat
  • Very good resistance to mineral oils, fuels and many chemicals
  • Very good resistance to ozone and weathering
  • Standard grades are less flexible at low temperature than NBR

Typical applications

  • High-temperature rotary shaft seals
  • Seals for chemical and petrochemical equipment
  • O-rings and static seals in hot or aggressive service

Advantages

  • Retains properties at elevated temperature
  • Broad fluid compatibility
  • Long-established choice for demanding rotary duty

Important selection considerations

  • Not suitable for every chemical — compatibility must be checked for the specific media
  • Low-temperature behaviour depends on the grade
  • Higher cost than NBR, so normally used where conditions require it

Temperature and pressure capability: depending on compound, design and application.

VMQ

Silicone Rubber

Silicone, VMQ

An elastomer with a wide working temperature range and good flexibility at low temperature.

General characteristics

  • Wide service temperature range, hot and cold
  • Very good resistance to ozone and weathering
  • Limited tear, abrasion and wear resistance
  • Compatibility with oils depends on the oil type and additives

Typical applications

  • Rotary seals in hot, lightly loaded applications
  • Static seals and gaskets
  • Seals exposed to low ambient temperatures

Advantages

  • Stays flexible across a wide temperature range
  • Good ageing and weathering behaviour
  • Soft compounds conform well to sealing surfaces

Important selection considerations

  • Generally not preferred for abrasive or highly dynamic duty
  • Check compatibility with the lubricant and its additives
  • Mechanical strength is lower than NBR, HNBR or FKM

Temperature and pressure capability: depending on compound, design and application.

HNBR

Hydrogenated Nitrile Butadiene Rubber

Hydrogenated nitrile, HSN

A hydrogenated nitrile that improves on NBR for heat, ozone and wear resistance.

General characteristics

  • Better heat and ozone resistance than standard NBR
  • Very good mechanical strength and wear resistance
  • Good resistance to mineral oils and many additive-rich lubricants
  • Good low-temperature flexibility, depending on grade

Typical applications

  • Rotary seals in demanding drives
  • Hydraulic seals in heavy-duty service
  • Seals exposed to additive-rich oils

Advantages

  • A step up from NBR without moving to FKM
  • Robust under dynamic load
  • Good ageing behaviour

Important selection considerations

  • Higher cost than NBR
  • Availability by profile and size can be narrower than NBR
  • Chemical compatibility should still be confirmed for the media

Temperature and pressure capability: depending on compound, design and application.

PTFE

Polytetrafluoroethylene

Virgin and filled grades

A fluoropolymer with very low friction and resistance to almost all industrial chemicals.

General characteristics

  • Very low coefficient of friction
  • Resistant to almost all industrial chemicals and fluids
  • Very wide service temperature range
  • Not elastic — needs a spring or elastomer energizer to maintain sealing force

Typical applications

  • PTFE spring energized seals
  • PTFE lip rotary seals
  • Piston seals, guide rings and wear rings in filled grades

Advantages

  • Suited to aggressive media and limited lubrication
  • Low friction and low stick-slip
  • Fillers such as glass, carbon or bronze adjust wear and load behaviour

Important selection considerations

  • Requires good shaft surface finish and hardness for dynamic duty
  • Installation needs more care than elastomer seals
  • Filler choice must suit the media and the mating surface

Temperature and pressure capability: depending on compound, design and application.

At a glance

General Material Comparison

An indicative, qualitative comparison for first orientation. Actual performance depends on compound, design and application.

Property NBRFKM / Viton™SiliconeHNBRPTFE
Mineral oil resistance GoodVery goodModerateVery goodExcellent
Heat resistance ModerateVery goodVery goodGoodExcellent
Low-temperature flexibility GoodLimitedVery goodGoodExcellent
Chemical resistance LimitedVery goodLimitedModerateExcellent
Wear resistance GoodGoodLimitedVery goodDepends on filler
Relative cost EconomicalHigherModerateModerate to higherHigher
Temperature / pressure rating Depending on compound, design and application.

Other elastomers and materials — such as polyurethane, EPDM and filled PTFE grades — are available where the application requires them.

Selection

What Material Selection Depends On

Share these details with an enquiry and our sales engineers can recommend a suitable material.

  • TemperatureNormal and peak, including heat generated at the sealing lip.
  • PressureSteady pressure, pressure peaks and vacuum.
  • SpeedShaft speed or stroke speed and frequency.
  • Chemical exposureProcess chemicals, cleaning agents and additives.
  • MediaOil, grease, water, fuel, gas or process fluid.
  • Shaft conditionSurface finish, hardness, run-out and wear.
  • Application environmentDust, moisture, weather and contamination.

Questions

Material Selection FAQs

Which is better for oil seals, NBR or FKM?

Neither is better in general. NBR is a widely used, economical choice for mineral oils and greases at moderate temperature. FKM is chosen when temperature or chemical exposure is higher. The right choice depends on the compound, the seal design and the application.

Can you give the temperature limit of a material?

Limits depend on the specific compound, the seal design and the application, so we do not publish general figures. Ratings are confirmed for the specific product when you send an enquiry.

When is PTFE used instead of an elastomer?

PTFE is considered where media are aggressive, lubrication is limited, friction must be low or temperatures are beyond what elastomers are suited to. Because PTFE is not elastic, it is used with a spring or elastomer energizer.

Knowledge Centre

Further Reading on Materials

All articles

Materials5 min read

NBR vs FKM Seals

NBR and FKM are the two most commonly specified seal elastomers. A qualitative comparison of where each one fits, and the questions to ask before choosing.

Read article

Materials5 min read

Choosing the Right Seal Material

An overview of the common seal materials, including NBR, HNBR, FKM, silicone, EPDM, polyurethane and PTFE, and the questions that decide between them.

Read article

Selection Guides5 min read

Seal Selection for High Temperature Applications

Heat shortens seal life in several ways. How to establish the temperature a seal really sees, which materials to consider, and how to reduce heat at the seal.

Read article

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Not sure which material you need?

Tell us the media, temperature, pressure and speed. Our sales engineers will recommend a suitable material and seal profile.

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