Heat-Resistant O-Rings: Temperature Ranges of the Materials
FFKM O-rings are the most heat-resistant: Standard compounds can withstand temperatures up to +270 °C in air, while high-temperature types can withstand temperatures up to +340 °C. Next are PTFE up to +250 °C, FEP-coated O-rings up to +205 °C, and FKM up to +200 °C; NBR has a limit of +120 °C. Hot water, steam, pressure, and cold temperatures shift these limits.
Operating temperature in air according to NH material data; NBR and EPDM for comparison.
- FFKM is the most heat-resistant O-ring material: Standard compounds can withstand temperatures up to +270 °C, while high-temperature grades such as ECOLAST NH5756 HT can withstand temperatures up to +340 °C.
- FKM covers a temperature range of −25 °C to +200 °C and is the cost-effective standard for high-temperature applications. The special FKMEX40 grade covers a temperature range of −40 °C to +225 °C.
- PTFE withstands temperatures up to +250 °C, while FEP-coated O-rings withstand temperatures up to +205 °C. Both are chemically resistant to virtually all substances, but PTFE is not elastic.
- NBR has a temperature limit of +120 °C, while peroxide-cured EPDM has a temperature limit of +150 °C.
- All values apply in air. In hot water, steam, and under pressure, the limit is often lower. Cold makes O-rings stiff, but this effect is reversible; heat damage, on the other hand, is permanent.
Temperature Ranges for O-Ring Materials
The table lists the operating temperature in air for all compounds in the NH product line, sorted by upper limit. NBR and EPDM are included for comparison. Clicking on a compound opens its data sheet.
| Material | Mixture | Operating Temperature | Primary Application |
|---|---|---|---|
| FFKMECOLAST | NH5756 HT | −15/+340 °C | High Temperature |
| FFKMECOLAST | NH5751 HT, NH7751 HT | −15/+330 °C | High Temperature |
| FFKMECOLAST | NH5755 HT | −15/+330 °C | Steam and hot water |
| FFKMECOLAST | NH5901 HT | −15/+320 °C | Oil and Gas, NORSOK M-710 |
| FFKMECOLAST | NH5750, NH7750 | −25/+270 °C | Standard, NH5750 with FDA approval |
| FFKMECOLAST | NH5760 LT | −40/+270 °C | Low Temperature |
| FFKMECOLAST | NH4700, NH7700 | −20/+270 °C | white, FDA and USP Class VI; NH4700 also 3-A |
| Solid PTFE | PTFE60 | −250/+250 °C | Non-elastic, static only, FDA |
| FKM Special Type | FKMEX40 | −40/+225 °C | Heat and Cold |
| FEP-coated FKM core | FEP-FKM | −25/+205 °C | Virtually universally chemically resistant, FDA |
| FEP-coated silicone core | FEP-Silicone | −60/+205 °C | Same as FEP-FKM, with additional cold resistance |
| FKMStandard | FKM75S, FKM75SFD | −25/+200 °C | Heat, oils, chemicals; FKM75SFD is FDA-approved |
| EPDM for comparison | peroxide-cured | −45/+150 °C | Water and steam |
| NBR for comparison | Nitrile rubber | −30/+120 °C | Mineral oil and greases |
Operating temperature in air according to the data sheet; for the definition of this term, see the glossary entry on temperature resistance. NBR and EPDM: These are comparative values; the exact limit depends on the specific compound. Other elastomers, such as silicone (VMQ), fluorosilicone (FVMQ), HNBR, and ACM, have their own temperature profiles; you can find them in the respective material articles.
Which material is suitable for which temperature?
Assume the highest temperature that occurs at the installation site, even if it occurs only briefly. After that, the medium and movement will further narrow down your choice. You can find a comparison of all criteria in the article “O-Ring Material: A Comparison of Materials.”
The standard choice for high temperatures, oils, and many chemicals, suitable for use from −25 °C to +200 °C. The special FKMEX40 type is rated for temperatures ranging from −40 °C to +225 °C. Learn more about FKM O-rings.
An FEP jacket, which is chemically resistant to virtually all substances, encloses an elastic core made of FKM or silicone. With a silicone core, the O-ring can be used at temperatures as low as −60 °C. Learn more about FEP O-rings.
PTFE is chemically nearly inert and cold-resistant down to −250 °C, but it is not elastic and is prone to cold flow. It is suitable for static sealing applications, such as flanges, where the ring does not need to return to its original shape. Learn more about PTFE O-rings.
ECOLAST NH5750 is elastic, highly resistant to a wide range of substances, and FDA-compliant. For the food and pharmaceutical industries, the white grades NH4700 and NH7700 are available and meet FDA and USP Class VI standards. Learn more about FFKM O-rings.
ECOLAST NH5751 HT and NH5755 HT are rated up to +330 °C, while NH5756 HT is rated up to +340 °C. For the oil and gas industry, the NH5901 HT is available up to +320 °C and is certified according to NORSOK M-710, including testing for explosive decompression. All types are listed on the ECOLAST website.
How Temperature Affects the O-Ring
An O-ring seals because it is pressed into the groove and uses its spring force to press against the sealing surfaces. If the sealing gap opens briefly—for example, during pressure surges—it must immediately spring back. Select a material and adjust the temperature: The simulator shows schematically when this is still possible.
Schematic illustration; thermal expansion is exaggerated for clarity. Limits: Operating temperature in air according to NH material data; FFKM Standard as NH5750, FFKM High Temperature as NH5756 HT, NBR and EPDM for comparison.
Heat: What's Happening Across the Border
Above the operating temperature, the polymer chains undergo cross-linking. The O-ring becomes harder, loses elasticity, and retains a permanent deformation, measurable as a high compression set. If it can no longer compensate for small movements of the components, the seal will fail. This damage is permanent.
Even within the specified limits, an O-ring ages more quickly the hotter it operates. As a rough rule of thumb, every 10 °C increase shortens its service life by about half. This rule is derived from the Arrhenius equation; testing laboratories use ISO 11346 to produce reliable service life predictions.
Thermal expansion: Allow for space in the groove
Elastomers expand about ten times as much as steel when heated. An O-ring that fits at room temperature can overfill the groove at +200 °C and be forced into the gap. Therefore, after pressing, allow for about 15–20% clearance in the groove; see O-Ring Grooves for more information. FFKM expands even more than FKM: If you switch from FKM to FFKM due to rising process temperatures, be sure to check the groove volume as well.
Lace counts too
The operating temperature listed in the data sheet applies to air. Cleaning-in-place (CIP), steam sterilization (SIP), and startup peaks often place a greater strain on the O-ring than normal operation. Therefore, use the highest temperature as a basis, not the average.
Recognizing Heat-Related Illnesses
Typical signs include fine cracks on the surface, a hard, brittle cross-section, and a flattened shape that no longer springs back. The article “High-Temperature O-Rings and Heat Damage” explains how to interpret these signs of damage and narrow down the causes.
Cold: What Happens Below the Threshold
In cold temperatures, the polymer chains move more and more slowly. The O-ring becomes stiffer and recovers more slowly; below the glass transition temperature, it is as hard as glass. As long as nothing is moving, it often still provides a seal. If pressure surges or vibrations open the sealing gap, it cannot recover quickly enough.
Unlike heat damage, the effects of cold are reversible: when the O-ring warms up, its elasticity returns. In addition, there is shrinkage. In cold temperatures, the O-ring contracts more than the metal parts surrounding it, causing the compression to decrease.
The TR-10 value
The TR-10 value, determined from the temperature recovery test in accordance with ISO 2921, indicates a compound’s resistance to low temperatures. A stretched specimen is frozen and then slowly warmed. TR-10 is the temperature at which the specimen has recovered 10% of its elongation. The lower the value, the more cold-resistant the material. For FKMEX40, this value is −30 °C, and the lower operating temperature is −40 °C.
A comparison of the materials best suited for cold environments:
Hot water, steam, and pressure push the boundaries
The operating temperature listed in the data sheet applies to air. In hot water and steam, hydrolysis and swelling further degrade the material, so the temperature limit is usually lower in these conditions. Peroxide-cured EPDM is the exception: based on our experience, it withstands temperatures up to 170 °C in hot water and steam.
Air: Operating temperature as specified in the data sheet. Hot water and steam: Empirical values provided without guarantee; if in doubt, test under actual operating conditions.
FKM is the best-known example: It withstands temperatures up to +200 °C in air, is not recommended for use in hot water, and can only be used in steam up to 120 °C. For water and steam, EPDM is generally the better choice; above that, FEP-coated O-rings, PTFE, or the ECOLAST Type NH5755 HT are suitable up to 270 °C. For more information, see the article “O-Rings for Hot Water and Steam.”
Oils and Chemicals
At high temperatures, media have a more severe corrosive effect on elastomers; swelling and leaching often occur simultaneously. Therefore, check the resistance at operating temperature, using the Media Resistance Tool, or in consultation with us.
High temperatures reduce an elastomer's resistance to deformation. Under pressure, the O-ring is then more easily pressed into the sealing gap. Keep the gap particularly narrow in high-temperature conditions and anticipate pressure spikes. For more information, see " Gap Extrusion " and " O-Rings Under Pressure."
Why Rubber Doesn't Melt
At what temperature does rubber melt? A vulcanized O-ring does not melt. Its polymer chains are chemically bonded into a network that does not break down when heated. In thermoplastics such as polyethylene, the chains are not bonded together. When heated, they slide past one another, causing the plastic to soften and flow.
If an elastomer gets too hot, it decomposes: First, it undergoes further cross-linking and hardens; then the chains break; and finally, the material carbonizes. As a seal, it will have failed long before that. Thermoplastic elastomers (TPE) are an exception: They are held together physically rather than chemically and can therefore be melted. For more on their structure, see Elastomers.
How Heat and Cold Resistance Are Tested
The temperature limits listed in the data sheet are based on standardized laboratory tests. These are the standards you'll encounter most frequently:
| Standard | Examination | Statement |
|---|---|---|
| ISO 188 | Heat aging: Specimens are stored at an elevated temperature in air; afterward, hardness, tensile strength, and elongation at break are compared to their initial values. | how much the material changes under heat |
| ISO 815-1 | Compression set: A specimen is compressed at room temperature or an elevated temperature; after unloading, the permanent deformation is measured. | how well the O-ring recovers after being exposed to heat |
| ISO 11346 | Aging tests at multiple temperatures, evaluated according to the Arrhenius or WLF models. | Service life at operating temperature and maximum operating temperature |
| ISO 2921 | TR Test: A stretched specimen is frozen and then slowly warmed; its recovery is measured. | Cold resistance, such as the TR-10 value |
| ISO 812 | Cold Brittleness: Specimens are subjected to an abrupt load at low temperatures. | the temperature at which the material fractures brittlely |
The standards specify test procedures, not limit values. The values achieved by a mixture are listed in its data sheet.
Frequently Asked Questions About Heat-Resistant O-Rings
Which O-rings are the most heat-resistant?
How heat-resistant is an NBR O-ring?
Up to what temperature can FKM withstand?
At what temperature does rubber start to melt?
Can rubber burn?
Does rubber contract in cold weather?
Which O-ring is suitable for hot water and steam?
What does the TR-10 value mean?
Selection Tools
