Neoprene (CR / Chloroprene) O-Rings

Neoprene is chlorobutadiene rubber (CR), polymerized from chloroprene. It is one of the oldest synthetic rubbers still in daily production, and it earns its place in the seal room for a specific combination of traits rather than for being best at any one of them. It resists ageing, weathering, and ozone attack, and it has high flame resistance, which is genuinely rare among the common seal compounds. The polar carbon-chlorine bond in the backbone is what gives it usable media resistance in simple mineral oils and greases.

Here is the honest framing, and it is the most useful sentence on this page: the chemical resistance of CR corresponds approximately to that of a nitrile with 18% acrylonitrile content. It behaves like a low-ACN nitrile. Decent in oil, not as oil-resistant as the standard 34% ACN Nitrile (NBR) you would buy for petroleum service. Nobody reaches for neoprene because it beats nitrile at oil. They reach for it because it does refrigerants, ammonia, ozone, weather, and flame in one compound.

Quick specs

Common names

Drawings and datasheets call the same polymer several different things. All of these mean neoprene:

• CR, the ASTM D1418 designation
• Chloroprene or polychloroprene
• Chlorobutadiene rubber, the formal Freudenberg naming
• Neoprene®, the original DuPont trade name that became the generic shop word

Mechanical properties

• Good mechanical strength that withstands dynamic loads
• Like natural rubber, CR tends to crystallize, which is why even unfilled vulcanizates show high strength
• Good resistance to ageing, weathering, and ozone attack
• High flame resistance, courtesy of the chlorine in the backbone
• Good resilience and tear resistance for a general-purpose compound
• Good abrasion resistance in dynamic and rubbing service
• Media resistance in simple mineral oils and greases from the polar carbon-chlorine bond

Limitations

The honest list. Neoprene is a specialist wearing a general-purpose suit:

• Middling oil resistance. It is roughly an 18% ACN nitrile. For serious petroleum service, standard Nitrile is better and cheaper. We will say so.
• Aniline point matters. CR handles mineral oils with a high aniline point. Low aniline point oils are more aromatic, and they attack it. If you only know the brand of the oil and not its aniline point, that is worth a phone call before you commit.
• Not for strong acids, aromatics, or esters. Use FKM (Viton®) or EPDM, depending on which one your fluid points at.
• Not for ketones or chlorinated hydrocarbons.
• Heat ceiling around +225°F. That is well below nitrile at +250°F and HNBR at +300°F. Neoprene is not the compound you choose when the problem is heat.
• Modest low-temperature reach, and the same crystallization that helps its strength can stiffen the seal on a long cold soak. A part that sits parked outdoors all winter is a different duty than one that cycles.

None of that is a knock on the material. It is the shape of it. Neoprene is chosen for its combination (refrigerants, ammonia, ozone, weather, flame resistance), not because it wins any single category outright.

Chemical compatibility

Handles well:

• Refrigerants, including ammonia and Freon®
• Mineral oils with a high aniline point, plus fats and greases
• Alcohol and glycol ether
• Water
• Diluted acids and bases
• Ozone, weather, and sunlight
• Silicone oils and greases

Attacks it:

• Strong acids
• Aromatic hydrocarbons and low-aniline-point (aromatic) oils
• Esters and ketones
• Chlorinated hydrocarbons

The oil story is the one people get wrong. “Neoprene is oil resistant” is true in the same way an 18% ACN nitrile is oil resistant: fine for simple mineral oil and grease, thin margin once the oil turns aromatic or the temperature climbs. Confirm your exact fluid on the Chemical Compatibility page or in the interactive Chemical Compatibility Chart.

A word on temperature ranges

Our published range for the neoprene we stock is -40°F to +225°F (-40°C to +107°C). That is the number to design around for standard commercial 70 duro CR.

Worth knowing: Freudenberg publishes a narrower -22°F to +230°F for its chloroprene compounds. That is not a contradiction, it is a different compound family and a more conservative window, particularly at the cold end where crystallization behavior gets a vote. The range moves by grade, and the difference between a good cold-weather CR and a generic one is real.

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, and a cold soak at rest is harder on CR than cold with motion. 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 Neoprene O-Rings

Inch (AS568):

• Neoprene (CR, Chloroprene) O-Rings

For metric sizes, metric Neoprene is available on request, contact us.

Need a durometer other than 70, an FDA grade, or an AMS3209 weather-resistant chloroprene? Ask us. Those are quoted rather than stocked, and we quote them regularly.

Variations and grades explained

Neoprene has fewer knobs than nitrile, but it is not one single material either.

By hardness (durometer)

• 70 Shore A: the standard for essentially all O-Ring service, and what we stock.
• Harder grades (80 to 90): for higher pressure and to resist extrusion through the gland gap.
• Softer grades (50 to 60): for low closing force, rough surfaces, and static gasket-like duty.

By polymer type

The chloroprene polymer itself is produced in a few families, and compounders pick among them for processing and property reasons:

• Sulfur-modified types: the traditional route, generally favored where tear strength and building tack matter.
• Mercaptan-modified types: better heat ageing and compression set than sulfur-modified, and the more common starting point for molded seals.
• Sulfur-free types: chosen where sulfur staining or metal contact is a concern.

In practice the seal compounder makes this call, not the buyer. It matters to you only when a drawing or a customer spec names one. If yours does, send it over and we will match it.

FDA grades

White or black FDA-compliant CR compounds are available for food and beverage contact. See FDA 21 CFR 177.2600 for what compliance actually means and what documentation comes with it.

AMS3209 weather-resistant chloroprene

If you buy electrical connector O-Rings, this is the callout you will see. AMS3209 covers weather-resistant chloroprene, and it is the spec behind a lot of MS-series connector seals.

Watch the trap: AS3209 is FKM. AMS3209 is chloroprene. One letter, two entirely different materials, and the mix-up shows up on real purchase orders. If your drawing says 3209, confirm which prefix before anyone buys anything. More on part-number specs in the mil-spec reference.

Standards and specifications

Neoprene O-Rings are supplied in the AS568 inch size range, with metric available on request. Useful callouts:

• ASTM D1418: designates the polymer as CR.
• ASTM D2000 / SAE J200: the line-callout system most commercial neoprene is bought to, covering its heat and oil resistance class.
• AMS3209: weather-resistant chloroprene, common on electrical connector O-Rings. See the mil-spec reference, and mind the AS3209 (FKM) versus AMS3209 (chloroprene) trap above.
• MIL-PRF-6855: Class 2 covers weather-resistant CR molded goods.

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 browse the full materials guide to compare compounds side by side.

Is Neoprene the right choice?

Three questions settle it:

1. Is a refrigerant or ammonia in the system? This is neoprene’s strongest case, and the reason most of it gets specified.
2. Does the seal live outdoors, or does it need to resist flame? Weather, ozone, and flame resistance in one affordable compound is a short list, and CR is on it.
3. Is the real problem oil or heat? Then it is probably not neoprene. Nitrile is better and cheaper for petroleum, and HNBR takes the heat to +300°F. For aggressive chemistry, go to FKM (Viton®) or EPDM.

Neoprene is a good answer to a specific question. When it is not the answer, we would rather point you at the compound that is.

Not sure whether Neoprene 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, the carbon-chlorine bond and its media effect, the 18% ACN nitrile equivalence, crystallization behavior, aniline point guidance, application list, and the -22°F to +230°F range: Freudenberg FST 2025 Technical Manual, ch. 2 (Materials and Process Engineering), §3.4, p. 55. Our published -40°F to +225°F range reflects the commercial CR market. The datasheet for your specific compound always governs; test parts in your actual service conditions before committing to a critical seal.