FFKM (Simriz® Perfluoroelastomer) O-Rings

FFKM (perfluoroelastomer) is the highest-performance sealing elastomer available, combining near-universal chemical resistance with extreme heat resistance. The reason is structural: FFKM is built from perfluorinated monomers, meaning the polymer contains no hydrogen at all. Almost every chemical attack on a rubber starts by going after a hydrogen site. Take the hydrogen away and there is nothing left to grab. Getting there takes special monomers plus special compounding and processing, which is also why the material costs what it costs.

What you end up with is an elastomer whose media and temperature resistance surpasses FKM (Viton®) by a wide margin and comes very close to PTFE, while still behaving like rubber. Freudenberg calls it “elastic PTFE”, and that is the cleanest description anyone has written: PTFE chemistry with elastomer recovery and sealing force. Freudenberg Sealing Technologies supplies its perfluoroelastomer line under the Simriz® trademark and is the only vertically integrated FFKM O-Ring manufacturer in the world, controlling the material down to the monomers. Where every other elastomer runs out of chemical or thermal headroom, FFKM keeps sealing.

Quick specs

Common names

The same family shows up on drawings and RFQs under several names. All of these mean FFKM:

• FFKM, the ASTM D1418 designation for perfluoroelastomers
• Perfluoroelastomer or perfluorinated rubber
• PFR or FFPM, older and ISO-adjacent designations
• “Elastic PTFE”, Freudenberg’s own shorthand for what the material actually is
• Simriz® (Freudenberg), the line we stock, and Kalrez® (DuPont), the name most buyers learned first

Kalrez® is a brand, not a material. When a drawing says Kalrez®, it is describing FFKM, and a Simriz® grade is normally the direct answer. Send us the callout and we will cross it.

Mechanical properties

• Near-universal chemical resistance, the best of any elastomer, by a distance
• Extreme heat resistance, past every other rubber on the shelf
• Excellent compression set resistance at temperature, which is what keeps sealing force alive
• Excellent resistance to steam, hot water, and CIP/SIP media in the right grade
• Very good resistance to rapid gas decompression in the RGD-formulated grades
• Very low outgassing and particulation in the high-purity semiconductor grades
• Rather moderate physical properties overall. This is the honest one: FFKM is a chemistry and heat material, not a strength material. Tensile, tear, and abrasion numbers are decent, not remarkable

Limitations

FFKM has almost no chemical weaknesses, so the honest list is about everything else. Freudenberg publishes these limits itself, and they are worth reading before you spend the money:

• It is very expensive. This is the main reason not to use FFKM, and it is a real reason. Nothing else on this page matters as much.
• If a cheaper compound already covers your chemistry, buy the cheaper compound. If FKM (Viton®), Viton® Extreme ETP, or Aflas® handles your fluid and temperature, use it and keep the money. We will tell you that instead of selling you the upgrade.
• Poor low-temperature flexibility. The worst of the common compounds. Standard grades stiffen well above where nitrile or silicone are still working. The Simriz® 481 low-temperature grade pulls this back to -30°C (-22°F), the best in the family, but that is still not a cold-service material.
• Rather moderate physical properties. For abrasive, high-pressure, or hard dynamic duty, FFKM is not the strength answer. Consider cast urethane where the chemistry allows, or keep the FFKM and support it with a back-up ring.
• Not easy to process. Perfluoroelastomer compounds are difficult to mix, mold, and cure. That is not trivia: it is why lead times, minimum order quantities, and tooling charges on non-stock FFKM sizes are real and not negotiable away.
• A few media still get through. Some fluorinated fluids and solvents, and molten alkali metals, will attack even FFKM. Nothing is truly universal.

Chemical compatibility

Handles well:

• Strong acids, including hot and oxidizing acids such as nitric and sulfuric
• Strong bases and caustics
• Ketones, esters, ethers, and aldehydes, the media that finish nitrile and FKM
• Amines, both aliphatic and aromatic
• Aromatic and chlorinated hydrocarbons, fuels, and solvents
• Steam, hot water, and superheated steam in the right grade
• Oxygen and plasma chemistries in the semiconductor grades
• Crude oil, sour gas, drilling and completion fluids, and hot lubricating oils
• Ozone, weather, and sunlight, indefinitely

Attacks it:

• Certain fluorinated fluids and solvents, including some fluorinated refrigerants and fluorocarbon-based media
• Molten alkali metals
• Sustained cold, which is a mechanical failure rather than a chemical one, but it will still cost you the seal

The practical rule: assume FFKM handles it, then verify the exceptions. Every other elastomer works the other way around. Check your exact fluid on the Chemical Compatibility page or in the interactive Chemical Compatibility Chart, and send us the media list if your process runs a cocktail rather than a single fluid.

A word on temperature ranges

Our published headline is up to +617°F (+325°C), by compound, and that last part is the whole story. FFKM’s temperature range is decided by the grade, not by the family.

• Freudenberg’s manual gives +14°F to +446°F (-10°C to +230°C) for standard types. That is the honest baseline for ordinary perfluoroelastomer, and it is where most of the lineup sits.
• Specific Simriz® grades go far past it. 498 is rated to +320°C (+608°F) and 502 to +325°C (+617°F). Those are datasheet numbers for those compounds, not a general FFKM claim. The datasheet governs, per grade.
• The low end is the genuine weakness. Standard FFKM does not like the cold, and no amount of compounding fixes that completely. Simriz® 481 reaches -30°C (-22°F), the best in the family. If you need real cold, you need a different family.

FFKM earns its place wherever temperatures prevail that no other elastic material can reach, or where near-universal chemical resistance is required. Both of those are grade decisions. And as always, any published range assumes the compound, the media, the pressure, the hardware, and the duty cycle all cooperate: heat plus an aggressive fluid plus a moving seal 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.

Why choose FFKM (Simriz®)

• Near-universal chemical resistance, including aggressive media that attack other elastomers such as ketones, esters, amines, and strong acids and bases.
• Extreme heat resistance combined with that chemical resistance in a single material.
• Elastomer recovery and sealing force in service conditions where PTFE and lesser elastomers fail.

Best for: near-universal chemical resistance combined with extreme heat, for semiconductor, chemical processing, oil and gas, aerospace, and pharmaceutical service. Avoid with: very little. The main limits are high cost, poorer low-temperature flexibility, and a few fluorinated solvents and molten alkali metals. Where the chemistry allows and cost matters, step down to Viton® Extreme ETP, which FFKM sits above for the most demanding service.

The Simriz® compound lineup

FFKM is not one material: each Simriz compound is tuned to a duty. This is the full lineup we carry, from the Freudenberg datasheets:

Temperature ranges are from the Freudenberg Simriz datasheets for each compound. Metric sizes: FFKM Metric O-Rings, or browse the whole family at Simriz® FFKM O-Rings.

General purpose: Simriz® 495 and 485

The two workhorses of the chemical process industry, both 75 duro with low compression set (495: 26 percent, 485: 23 percent, 70 h at 204°C). 495 shines in strong acids and oxidizers; Freudenberg’s data shows it beating competitors in 69 percent nitric acid soak at 80°C out to 1,000 hours. 485 leans toward superheated steam and hot water. Typical homes: pumps, valves, mechanical seals, paint spray equipment, dispensers, and vacuum components.

The flagship: Simriz® 498

Freudenberg calls 498 “the ultimate FFKM material,” and its chart backs it up: 80 duro, service from -5°C to +320°C, with top marks across solvents, acids, bases, amines, and steam at once. If one FFKM has to cover nearly every application in the plant, this is the one. Also the reference compound in Freudenberg’s steam and compression-set comparisons.

Oil and gas: Simriz® 134 and 502

Both 90 duro for extrusion resistance at high pressure, both built to survive rapid gas decompression (RGD), the blistering that kills seals when high-pressure gas drops suddenly (see Failure Analysis). 134 is NORSOK M-710 (Rev. 2) certified, tested in 90/10 methane/CO2 at 15 MPa with no cracks, blisters, or holes, and handles steam sterilization and autoclaving. 502 adds the top of the temperature range (+325°C) for drilling, wireline, perforating, completion tools, and steam-injection/SAGD service.

Low temperature: Simriz® 481

Standard FFKM stiffens in the cold. 481 stays flexible to -30°C (-22°F), the lowest service temperature in the lineup, while keeping the broad FFKM chemical resistance, for chemical-process duty that sees cold ambient or cold media.

Food, beverage, and pharma: Simriz® 484

Compounded for regulated hygienic service: FDA compliant, USP Class VI compliant, 3-A Sanitary, and ADI-free, with strong resistance to CIP/SIP clean-in-place and sterilize-in-place media. See our FDA food contact, USP Class VI, and 3-A Sanitary certification pages for what those approvals mean.

Semiconductor: Simriz® 486CP and 508/508CP

Wafer processing runs plasma chemistries that eat ordinary elastomers and cannot tolerate particles. 486CP is a white, high-purity, plasma-resistant grade with post-process cleaning and packaging standard, for CVD, PVD, etch, and ash chambers. 508/508CP is the step up: off-white, best thermal stability in the family by TGA, and standout resistance in high-energy oxygen and remote plasma, for chamber lids, windows, and gate/pendulum/isolator valves. The CP suffix means cleaned and packaged for the fab.

Premium aerospace: Simriz® 501 and Z7257

Freudenberg’s AMS7257 materials (see the mil-spec reference), produced in NADCAP-certified production. 501 is the next generation beyond the proven Z7257, tested well past the spec: both carry a high-temperature operating recommendation of +610°F versus the AMS7257 default of +554°F, and 501 shows flight-test-backed compressive stress retention at 300°C. Built for bleed-air systems, gas-turbine lubrication (including degraded MIL-PRF-23699 HTS oils), high-temperature propulsion, and strong-oxidizer control devices.

Shop FFKM O-Rings

Every Simriz® grade we stock, by compound and size:

Inch (AS568):

• Simriz® FFKM O-Rings, the full family
• Simriz® 495, 75 duro, acids and oxidizers
• Simriz® 485, 75 duro, steam and hot water
• Simriz® 498, 80 duro, the all-rounder
• Simriz® 134, 90 duro, RGD / NORSOK M-710
• Simriz® 481, 75 duro, low temperature
• Simriz® 484, 75 duro, FDA / USP Class VI / 3-A
• Simriz® 486 / 486CP, 75 duro, semiconductor
• Simriz® 501, aerospace AMS7257

Metric:

• FFKM Metric O-Rings

Special quote: Simriz® 502 and Simriz® 508 / 508CP are quoted to order. Ask us.

Need a size, durometer, or compound that is not listed? A great deal of the FFKM world is made to order, and we quote it regularly. Sizes follow the standard AS568 and metric size charts.

Standards and specifications

FFKM O-Rings are supplied in the full AS568 inch size range and common metric sizes. FFKM is the generic ASTM D1418 designation for perfluoroelastomers; AMS7257 is the aerospace FFKM spec, and Simriz 501/Z7257 are Freudenberg’s materials on that QPL. Certifications by grade include NORSOK M-710 (134), FDA / USP Class VI / 3-A (484), and high-purity semiconductor processing (486CP, 508CP). If your drawing calls out a compound or approval, tell us and we will match it.

Useful callouts and where to read more:

• ASTM D1418: designates the polymer as FFKM.
• AMS7257: the aerospace perfluoroelastomer spec. See the mil-spec reference for how the QPL system works.
• NORSOK M-710: the oil and gas RGD and aging qualification carried by Simriz® 134.
• FDA 21 CFR 177.2600: see FDA food contact.
• USP Class VI: see USP Class VI.
• 3-A Sanitary Standards: see 3-A Sanitary.

Everything ships 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, Design & Engineering for the gland around the seal, or Materials to compare the whole compound shelf.

Is FFKM the right choice?

Three questions settle it:

1. Does anything cheaper cover your chemistry and temperature? If FKM (Viton®), Viton® Extreme ETP, or Aflas® handles it, buy that and save the money. This is the first question for a reason.
2. Are you past +450°F, or running media that eats every other elastomer? Then FFKM is not a luxury, it is the only elastic material left. Pick the grade, not the family.
3. What does failure cost? An FFKM O-Ring is expensive. An unplanned shutdown, a scrapped wafer lot, a contaminated batch, or a fishing job downhole is far more expensive. That arithmetic is what justifies the price, and when it does not, we will say so.

If the answer is still yes, the grade is the next decision, and it is the one that actually matters. Send us the service conditions: media, temperature, pressure, whether the seal moves, and any approval your drawing calls out.

Not sure whether FFKM is worth it for your application, or which Simriz® grade fits? 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, and we will tell you when a cheaper material will do the job. We make getting O-Rings easy.

Compound data from the Freudenberg Sealing Technologies Simriz® datasheets on file (134, 481, 484, 485, 486CP, 495, 498, 501/Z7257, 502, 508/508CP). The datasheet for your compound and revision governs; ask us for a copy with your quote.

Perfluorinated (hydrogen-free) polymer chemistry, the “elastic PTFE” characterization, the processing, low-temperature, and physical-property limitations, the +14°F to +446°F range for standard types, and the industry application list: Freudenberg FST 2025 Technical Manual, ch. 2 (Materials and Process Engineering), §3.4, p. 68. Grade-specific temperature ranges beyond the standard-type figure come from the individual Simriz® datasheets. Test parts in your actual service conditions before committing to a critical seal.