O-Ring Chemical Compatibility Guide | Seal Material Resistance
Choosing the correct sealing material is just as important as selecting the correct seal size. An O-ring or gasket may be dimensionally correct but can still fail rapidly if the elastomer is incompatible with the fluid, chemical or cleaning media it contacts. Chemical attack can cause swelling, shrinkage, softening, hardening, loss of tensile properties and permanent deterioration of sealing performance. The extent of these changes depends not only on the chemical itself, but also on concentration, temperature, pressure, exposure time and the specific compound formulation.
This chemical compatibility guide compares the resistance of commonly used O-ring and seal materials including NBR, HNBR, EPDM, FKM, silicone, FFKM and PTFE. It is intended as a starting point for material selection, with detailed chemical resistance data available in our downloadable compatibility chart.
How Chemical Compatibility Is Rated
Chemical compatibility ratings provide a practical indication of how a sealing material is expected to respond when exposed to a particular fluid or chemical. Compatibility is commonly classified using a rating system ranging from highly resistant through to unsuitable. These ratings may consider changes such as volume swell, hardness, tensile strength, elongation and general deterioration after exposure.
A compatibility rating should not be treated as a simple guarantee that a material will or will not work. Published data is normally based on specific test conditions, while actual seal performance depends on the compound formulation and operating environment.
For this guide, the following classifications are used:
| Rating | Classification | General Interpretation |
|---|---|---|
| A | Excellent | High resistance expected; generally suitable under the stated operating conditions |
| B | Good | Minor material changes may occur; generally suitable for many applications |
| C | Limited | Noticeable swelling, softening or property changes may occur; application-specific evaluation required |
| D | Not Recommended | Significant material deterioration may occur; an alternative sealing material should normally be selected |
| — | No Data | Insufficient information available; compatibility should be confirmed before use |
Higher temperatures often accelerate chemical attack and can substantially change the suitability of a material. Concentration, exposure duration, pressure and whether the seal operates dynamically or statically can also influence performance.
For temperature-specific information, see our Elastomer Temperature Range Guide.
NBR (Nitrile) Chemical Compatibility
NBR, also known as nitrile rubber or Buna-N, is one of the most widely used general-purpose O-ring and sealing materials. It offers particularly good resistance to petroleum-based oils, mineral oils, hydraulic fluids, greases and many hydrocarbon fuels.
This combination of chemical resistance, mechanical properties and cost makes NBR widely used in hydraulic, pneumatic, automotive and general industrial sealing applications.
NBR is generally less suitable for ozone, prolonged outdoor weathering, many strong oxidising chemicals and certain polar solvents. Its compatibility with fuels can also depend on the fuel composition and acrylonitrile content of the particular NBR compound.
For applications involving oils and conventional hydraulic fluids, NBR is often the first material considered, provided the temperature and environmental conditions are also suitable.
HNBR Chemical Compatibility
HNBR, or hydrogenated nitrile rubber, is produced by chemically modifying NBR to improve its resistance to heat, oxidation and ageing while retaining much of nitrile’s useful resistance to oils and fuels.
HNBR offers good resistance to petroleum oils, many hydraulic fluids, fuels and lubricants, together with improved resistance to ozone and elevated temperatures compared with conventional NBR. It is widely used in demanding automotive, oil and gas, industrial and fluid-power applications where standard nitrile cannot provide sufficient temperature or environmental resistance.
HNBR is not universally chemically resistant, however, and compatibility with strong acids, aggressive solvents and particular process chemicals should be confirmed against the specific compound and operating conditions.
EPDM Chemical Compatibility
EPDM offers excellent resistance to water, hot water, steam, ozone, weathering and a wide range of dilute acids, alkalis and polar chemicals. These properties make it one of the most important sealing elastomers for hygienic processing and outdoor applications.
EPDM is commonly specified for food and beverage processing, dairy equipment, pharmaceutical systems, water applications and CIP/SIP cleaning environments, subject to the temperature and chemical concentration involved. Its principal limitation is poor resistance to petroleum oils, hydrocarbon fuels and many mineral-oil-based lubricants. EPDM should therefore generally not be selected where sustained contact with hydrocarbon oils or fuels is expected.
Different EPDM formulations can vary considerably in steam, chemical and food-contact performance, so the specific compound should be confirmed for demanding applications.
FKM (Viton) Chemical Compatibility
FKM fluoroelastomers are high-performance sealing materials offering excellent resistance to many oils, fuels, hydrocarbons and aggressive chemicals, together with strong high-temperature capability. FKM is widely used in fuel systems, chemical processing, aerospace, automotive and industrial applications where both chemical and thermal resistance are required.
Compared with NBR, FKM generally provides a much broader operating envelope for hydrocarbons and elevated temperatures. However, standard FKM compounds can have limitations with hot water, steam, amines, certain organic acids and some polar chemicals. Different FKM polymer types and compound formulations can provide significantly different chemical resistance. Applications involving aggressive media should therefore be assessed against the specific grade rather than FKM as a material family alone.
For continuous hot-water and steam applications, correctly specified EPDM or specialist FKM grades may be more appropriate depending on the process conditions.
Silicone Chemical Compatibility
Silicone rubber provides an exceptionally broad temperature range and retains flexibility at temperatures where many conventional elastomers become too stiff to seal effectively. It is widely used in food, beverage, pharmaceutical, medical and other clean applications because suitable silicone compounds can also offer excellent purity and regulatory characteristics.
From a chemical-resistance perspective, silicone performs well with water and many dilute aqueous solutions but is generally less resistant to petroleum oils, fuels, concentrated acids, alkalis and many solvents than materials such as FKM or FFKM.
Silicone should therefore be selected primarily where temperature capability, flexibility, cleanliness or regulatory requirements are important, with chemical compatibility confirmed separately for the process media.
FFKM Chemical Compatibility
FFKM, or perfluoroelastomer, provides the broadest chemical resistance of the commonly used elastomer families while retaining the elastic sealing behaviour required for O-rings and other rubber seals. Depending on the compound grade, FFKM can offer exceptional resistance to aggressive acids, bases, solvents, hydrocarbons, amines and other process chemicals, together with very high temperature capability.
These properties make FFKM particularly valuable in semiconductor manufacturing, pharmaceutical processing, chemical production, oil and gas and other critical applications where chemical exposure would rapidly degrade conventional elastomers.
FFKM is not a single universal material. Different grades are formulated for different chemical and temperature environments, and certain highly reactive media can still require specialist compounds. Cost is also substantially higher than conventional elastomers, so FFKM is typically specified where its performance advantages justify the additional material cost.
PTFE Chemical Compatibility
PTFE is a fluoropolymer rather than an elastomer and provides exceptionally broad chemical resistance across a wide temperature range. It is resistant to most commonly encountered industrial chemicals and is frequently selected for aggressive chemical environments where conventional rubber compounds are unsuitable. PTFE is widely used for gaskets, envelope gaskets, valve components, back-up rings and specialised sealing elements.
Unlike elastomers, PTFE has very little elastic recovery. This means it behaves differently under compression and is not normally a direct replacement for a conventional rubber O-ring without changes to the seal design.
PTFE envelope gaskets combine the chemical resistance of a PTFE contact surface with the resilience of an elastomeric core and are widely used in hygienic and chemical-processing applications.
For exceptionally aggressive applications, compatibility should still be confirmed against the exact chemical, concentration and temperature.
Choosing the Right O-Ring & Seal Material
There is no single sealing material that is best for every chemical environment.
As a general starting point:
- NBR is commonly selected for petroleum oils, lubricants and hydraulic fluids.
- HNBR provides improved temperature, ozone and ageing resistance while retaining useful oil resistance.
- EPDM is particularly suited to water, steam, weathering and many hygienic-process applications.
- FKM provides strong resistance to hydrocarbons, fuels and many aggressive chemicals at elevated temperatures.
- Silicone is primarily selected for its exceptional temperature range, flexibility and purity characteristics.
- FFKM provides extremely broad chemical and high-temperature resistance for demanding applications.
- PTFE offers exceptional chemical resistance where an elastomeric seal is not required.
These descriptions are only a starting point. Final material selection should consider the exact chemical or mixture, concentration, minimum and maximum temperature, pressure, exposure duration, cleaning process and whether the seal operates statically or dynamically.
International Seal can assist with material and compound selection. Provide the chemical or process media, concentration, operating temperature, pressure, seal type and application conditions, and we can help identify suitable sealing materials for further evaluation.