O-Ring Temperature Guide

Jump to the temperature chart TR-10 & high-temp tests Chemical Compatibility Chart

Temperature and fluid together decide the compound. A nitrile ring that lives forever in room-temperature hydraulic oil can harden, crack, or take a set if the same oil runs hot—or go stiff and leak if the system sits at −40°F overnight. This guide collects the handbook’s published temperature ranges, explains what those numbers mean, and shows how to shortlist a family before you open the Chemical Compatibility Chart.

How to read an O-Ring temperature range

Published ranges (for example −40°F to +250°F) are engineering windows for typical standard compounds, not a guarantee for every grade or every duty.

Practical rule: design for the hottest continuous and coldest start-up the seal will see in the real fluid—not the brochure maximum in dry air.

Compound temperature chart

Ranges below match the handbook Materials overview for standard stocked families. Specialty grades can run wider or narrower.

Low-temperature service

At the cold end the risk is stiffness and loss of seal force, not melting. The ring may look fine on the bench and still leak when the machine starts cold.

Strong cold performers (typical standard grades)

• Silicone and fluorosilicone
• Butyl
• Cast urethane (very low)
• EPDM (good low end for water systems)
• Nitrile / HNBR around −40°F (use low-temp NBR when you need colder)

Watch-outs

• Standard FKM gets stiff near −20°F; specialty low-temp FKM exists but is a different buy
• Harder durometers (90 Shore A) feel the cold sooner than 70 Shore A
• Dynamic cold seals need extra care—lubrication and squeeze matter more

If cold start is the driver, name the lowest temperature on the RFQ, not only the operating average.

High-temperature service

At the hot end the risks are compression set, hardening, cracking, and chemical attack that speeds up with heat.

Heat + fluid beats heat alone. Compatibility charts are usually near room temperature. A compound rated “1” in a fluid at 70°F can fail in the same fluid at 300°F. When you are near an edge, ask for grade data or a test—not only the family name.

Steam vs dry heat

Temperature, hardness, and extrusion

Heat softens elastomers. Soft rings extrude into the gap more easily. If the system is both hot and high pressure, plan on:

• A compound with enough heat resistance
• Adequate Shore A hardness and/or a back-up ring
• A gland that still fits after thermal growth

See Shore A Hardness for the extrusion-gap chart.

Static vs dynamic at the extremes

Lab tests behind the temperature numbers

Datasheet temperature claims are not guesses. Labs run standardized cold and heat tests so you can compare compounds. Two families matter most for seals: TR-10 (cold flexibility) and high-temperature aging / compression set (hot recovery).

TR-10 (temperature retraction)

TR-10 comes from the temperature-retraction test (ASTM D1329, also ISO 2921). It is the cold number seal people trust most for O-Rings.

How the test works (plain version)

1. A rubber specimen is stretched (commonly 50%, sometimes 25% or 100% depending on the lab method).
2. It is locked elongated and frozen cold enough that it cannot snap back.
3. One end is released; the specimen stays stretched while it is still glassy.
4. The chamber is warmed at a controlled rate.
5. As the rubber softens, it retracts. The temperature where it has recovered 10% of the stretch is TR-10 (TR10). Labs also report TR70 (70% retraction); the gap between TR-10 and TR70 grows when a polymer likes to crystallize.

How the industry uses TR-10 for seals

That is why Parker and other seal houses treat TR-10 as a better low-temp guide for compression seals than older “brittle point only” stories. A published low-temp rating on an O-Ring datasheet is often TR-10 with a static margin baked in—ask for the raw TR-10 if you are designing to the edge.

Related cold tests you may see

• Glass transition (Tg) — temperature where the polymer goes glassy (e.g. DSC / ASTM D3418). Useful physics; TR-10 is closer to seal recovery in a gland.
• Brittleness / crack tests (e.g. ASTM D2137) — when the rubber shatters under impact while cold. Important for abuse, less complete than TR-10 for squeeze seals.

High-temperature tests

Heat does not only “melt” rubber. It drives chemical aging (oxidation, cross-link changes) and loss of elastic memory. The common datasheet tests:

Compression set (ASTM D395 / ISO 815)

The most important hot-seal number for O-Rings.

1. Compress a button or O-Ring section a fixed amount (often 25% deflection).
2. Hold it in an oven at a stated temperature and time (examples: 22 h or 70 h at 100°C, 125°C, 150°C, 200°C—whatever the spec calls).
3. Release, wait (often ~30 minutes), remeasure thickness.
4. Report compression set %: how much of the squeeze the rubber did not give back.

Lower set is better. High set means the ring permanently flattens and loses sealing force—classic heat failure even when the part is not “burned up.”

Heat aging in air (ASTM D573 / related oven methods)

Unconstrained (or fixture-aged) specimens sit in a hot-air oven for a set time. Labs then remeasure:

• Hardness (Shore A)
• Tensile strength
• Elongation at break
• Sometimes modulus

Large hardness rise + elongation drop usually means the compound is cooking—hardening and cracking risk in service.

Fluid aging at temperature

The same physical checks after soak in oil, fuel, water, or process fluid at elevated temperature. Volume change (swell/shrink) is reported with the property shifts. This is why a room-temp compatibility “1” is not enough for a hot system: heat accelerates attack.

Other heat-related numbers

Reading a datasheet with these tests

1. For cold: find TR-10 (and whether the low-temp claim is TR-10 or TR-10 minus a static margin).
2. For heat: find compression set at a temperature near your continuous max, plus air-oven and fluid-aged property changes.
3. Match test time and temperature to your duty. A great 22 h / 100°C set result does not prove 5,000 hours at 150°C in hot oil.
4. Prefer grade data over family folklore when you are within about 25°F of a limit.

Quick selection path

1. Write down min start-up and max continuous temperatures (and whether steam, oil, or dry).
2. Shortlist families from the chart above that cover both ends.
3. Confirm the fluid on the Chemical Compatibility Chart.
4. Set durometer and size (Shore A, Master O-Ring Size Chart).
5. If you are within ~25°F of a published limit, or the duty is dynamic + hot, ask for the grade datasheet (TR-10, compression set, heat/fluid aging)—or contact us.

Related

• Materials / compound guide
• Chemical Compatibility Chart
• Compatibility overview
• Shore A Hardness
• Failure Analysis