HNBR (Hydrogenated Nitrile / HSN) O-Rings

HNBR is what you get when you take the workhorse of the sealing world and fix its two biggest weaknesses. It starts as standard Nitrile (NBR) and goes through a hydrogenation step that saturates the double bonds in the butadiene backbone, reducing them to roughly 1 to 7 percent of what they were. Those double bonds are exactly where heat, oxygen, and ozone attack the polymer. Remove them and you keep every bit of nitrile’s oil and fuel resistance while gaining about 50°F of heat headroom, far better weathering, and higher strength that holds up when hot.

That is the whole pitch: same fluids, same sizes, longer life. It is why HNBR is the default seal in automotive air conditioning and a staple in the oil field, and why it is usually the right answer when standard nitrile keeps coming out hard and cracked.

Quick specs

Common names

The same material shows up on drawings under a pile of different names. All of these mean HNBR:

• HSN (highly saturated nitrile)
• Hydrogenated nitrile or hydrogenated Buna-N
• HNBR, the ASTM D1418 designation
• Therban® (Arlanxeo) and Zetpol® (Zeon), the two main polymer trade names

Mechanical properties

• Excellent heat and oxidation stability, especially in peroxide-cured grades
• High mechanical strength that holds at temperature, where standard nitrile softens
• Excellent abrasion and fatigue resistance, better than NBR
• Good dynamic performance, which is why it is used in rod, piston, and rotary shaft seals
• Good compression set resistance
• Very good weather, ozone, and UV resistance (the hydrogenation is what buys this)
• Good resistance to rapid gas decompression in the right grades

Limitations

The honest list. HNBR is an upgrade over nitrile, not a universal seal:

• Not for glycol brake fluid (DOT 3, 4, 5.1). Use EPDM.
• Not for ketones, esters, or aldehydes. Use EPDM or FFKM.
• Not for chlorinated or aromatic hydrocarbons. Use FKM (Viton®).
• Not for phosphate-ester hydraulic fluids (Skydrol®). Use EPDM.
• Limited in aromatic fuels, the same weakness it inherits from nitrile.
• Runs out of heat around +300°F. Above that, go to FKM at +400°F, Aflas® at +450°F, or FFKM.
• Costs more than standard nitrile. On a job that never sees heat, wear, weather, or gas, that premium buys you nothing. See HNBR vs Buna-N for where the money is worth it.

Chemical compatibility

Handles well:

• Petroleum oils, greases, and hydraulic fluids, including hot oil
• Crude oil and oilfield fluids
• Sour gas (hydrogen sulfide) in the right grade
• Air conditioning refrigerants, including R134a
• Ethylene glycol coolants and di-ester lubricants
• Water and steam better than standard nitrile, though not as well as EPDM
• Silicone oils and greases, alcohols, carbon dioxide
• Ozone, weather, and sunlight

Attacks it:

• Glycol brake fluids, ketones, esters, aldehydes
• Chlorinated and aromatic hydrocarbons
• Phosphate esters, strong oxidizing acids

Media resistance is broadly comparable to standard nitrile: the hydrogenation buys heat, strength, and weathering, not a different chemical personality. Confirm your exact fluid on the Chemical Compatibility page or in the interactive Chemical Compatibility Chart.

A word on temperature ranges

Published ranges are approximations, and HNBR’s range moves more than most because it is a family, not a single recipe. The numbers on this page describe standard commercial grades: about -40°F to +300°F. Around that center:

• Low-temperature grades stay flexible to roughly -50°F, at some cost to heat life.
• Peroxide-cured high-heat grades are rated by some suppliers to +325°F and beyond, in the right media.
• Freudenberg publishes -4°F to +302°F for its HNBR compounds, a more conservative window than the commercial norm.

Any published range assumes the compound, the media, the pressure, the hardware, and the duty cycle all cooperate. Heat plus an aggressive fluid shortens life faster than heat alone. If your application sits near an edge, send us the conditions and we will pull the datasheet for the actual compound rather than guess from a chart.

Shop HNBR O-Rings

Every HNBR variation we stock, by grade and size:

Inch (AS568):

• HNBR (HSN) Hydrogenated Nitrile, Green/Black

Metric:

• HNBR Metric 70 Duro, Green/Black

Need a durometer, color, or grade that is not listed, or an FDA or RGD-rated HNBR? Ask us. Much of the HNBR world is made to order, and we quote it every week.

Variations and grades explained

HNBR is not one material. The grade is chosen by duty, which is why the temperature limit and the fine print on chemical resistance are always grade-specific.

By degree of hydrogenation

The key number is residual double bond content (RDB): how much of the butadiene backbone is left unsaturated after hydrogenation.

Lower RDB means more heat resistance. It is the single biggest lever in the material.

By acrylonitrile (ACN) content

HNBR inherits the same ACN trade-off as standard nitrile: more acrylonitrile means better oil and fuel resistance but stiffer behavior in the cold. Low-ACN grades are the ones that reach toward -50°F.

By cure system

• Peroxide cured: the best heat resistance and compression set at temperature. The default for hot service.
• Sulfur cured: possible only on higher-RDB grades. Better low-temperature flexibility, lower heat ceiling.

By hardness (durometer)

• 70 Shore A: the standard for most applications, and what we stock.
• 90 Shore A: for high pressure and to resist extrusion through the gland gap.
• The family runs 50 to 90 Shore A; softer and harder grades are quoted to order.

Related and modified HNBR

• Carboxylated HNBR (XHNBR or HXNBR): carboxyl groups added for a large jump in abrasion and tear resistance. Built for dynamic, high-wear oilfield service.
• RGD-resistant grades: formulated to survive rapid gas decompression in high-pressure gas.
• Low-temperature grades: reach roughly -50°F by trading away some heat life.
• FDA grades: available for food and beverage contact; see FDA 21 CFR 177.2600.

Standards and specifications

HNBR O-Rings are supplied in the full AS568 inch size range and common metric sizes. Useful callouts:

• ASTM D1418: designates the polymer as HNBR.
• ASTM D2000 / SAE J200: the line-callout system most commercial HNBR is bought to, typically in the DH type and class range that covers its heat and oil resistance.
• No dedicated military O-Ring spec exists for HNBR. Unlike nitrile, FKM, fluorosilicone, silicone, and EPR, HNBR has no M-number part standard of its own, so aerospace and defense work calls it out through ASTM D2000 or a customer drawing. See the mil-spec reference for the compounds that do have one.

If your drawing calls out a specific spec or compound, tell us and we will match it, with a Certificate of Conformance and lot traceability under our ISO 9001:2015 system.

Typical applications by industry

See O-Rings by Industry for the wider picture, or Design & Engineering for the gland around the seal.

Is HNBR the right upgrade?

Three questions settle it:

1. Does the seal run hotter than about 250°F? Standard nitrile is done. HNBR is not.
2. Is it dynamic, high pressure, or abrasive? HNBR’s strength and abrasion resistance pay for themselves.
3. Is ozone, weather, sour gas, or rapid decompression in play? All four point to HNBR.

If none of those apply and the fluid is ordinary oil at ordinary temperature, standard Buna-N already does the job for less. We will tell you that rather than sell you the upgrade. The full side-by-side is in HNBR vs Buna-N Nitrile O-Rings.

Not sure whether HNBR covers your fluid and temperature? Send us the conditions: the media, the temperature, the pressure, and whether the seal moves. We will spec the compound and the size with you. We make getting O-Rings easy.

Polymer chemistry, residual double bond levels, cure-system behavior, property set, and the -4°F to +302°F range: Freudenberg FST 2025 Technical Manual, ch. 2 (Materials and Process Engineering), §3.4, p. 69. Commercial grade ranges reflect the wider HNBR market. The datasheet for your specific compound always governs; test parts in your actual service conditions before committing to a critical seal.