FFKM O-rings: the highest-performing O-ring material
FFKM O-rings combine two properties that no other elastomer offers at the same time: near-universal media resistance and very high temperature resistance. They seal reliably where NBR, EPDM or FKM have long since failed.
- FFKM is the most chemical- and temperature-resistant elastic sealing material, near-universally resistant.
- Used from −40 to +340 °C depending on the compound, standard types up to +270 °C.
- Fully elastic, unlike PTFE or FEP, and therefore usable as a flange, piston and rod seal.
- The only real drawback is the price. FFKM pays off where other materials fail on temperature or medium.
- Available from NH O-RING under the ECOLAST brand, over 5,000 sizes from stock and with no minimum order quantity.
What is FFKM?
FFKM is the abbreviation for perfluoro-rubber, also called perfluoroelastomer. It denotes a fully fluorinated synthetic rubber used primarily as a high-performance sealing material. The older designation FFPM refers to the same material; today the abbreviation FFKM is the common one.
The decisive point lies in the chemical structure. FFKM consists almost entirely of carbon-fluorine bonds, one of the strongest bonds in organic chemistry. This is why even aggressive media barely attack the material. FKM (fluoroelastomer), by contrast, is only partially fluorinated and still contains hydrogen in the molecule, which makes it more sensitive.
How to read the graphic: In FFKM, every position on the carbon chain carries a fluorine atom (F). There are no more hydrogen atoms and therefore no weak point. The fluorine atoms envelop the chain seamlessly, and that is the green fluorine shield.
This is exactly what makes FFKM near-universally resistant, including against hot water, steam, amines and aggressive chemicals, and that up to +270 °C and higher. Unlike PTFE, FFKM remains a true elastomer with restoring force.
The key properties
- Near-universal media resistance: resistant to the vast majority of acids, alkalis, solvents, fuels, oils and hot steam. Check specific media in the media resistance tool.
- Temperature resistance: from −40 °C to +340 °C depending on the compound.
- Fully elastic: unlike PTFE or FEP-encapsulated O-rings, FFKM stays elastic and is suitable as a flange, piston and rod seal.
- Hardness: 70 to 90 Shore A depending on the compound.
- Approvals: FDA, USP Class VI, 3-A and EC 1935/2004 for food, pharma and hygiene, depending on the compound.
- Shelf life: 15 years with proper storage in accordance with DIN 7716.
The only notable drawback is the price. Perfluoro-rubber is very complex to manufacture, and the raw material costs many times more than common materials. FFKM pays off wherever no other material meets the requirements and where reliability and service life matter.
Temperature ranges compared
Among the elastic sealing materials, FFKM covers the highest continuous-service temperature range. The graphic compares the standard types of the four NH high-performance materials with six common elastomers.
Continuous-service temperatures of typical sealing materials as a standard compound, NH materials in coral. Values are guide figures depending on the compound; the relevant data sheet is authoritative.
Why is FFKM near-universally resistant?
Every elastomer material reveals through its name what it is built from. The two "F"s in FFKM stand for fluorine. Fluorine forms an exceptionally stable bond with carbon. Because FFKM is fully fluorinated, media find hardly any point of attack.
Which material withstands how much, from EPDM through FKM to FFKM (ECOLAST), separated by hot water and steam.
To the hot-water and steam table →There are only a few exceptions where you should be careful:
- Media with a high fluorine content, such as elemental fluorine (like attacks like).
- Molten alkali metals.
In almost all other cases, FFKM can be used without chemical concern.
FFKM vs. FKM: the direct comparison
FKM (often known under the brand name Viton) is the proven standard for demanding applications. FFKM goes a clear step further.
| Characteristic | FKM | FFKM |
|---|---|---|
| Fluorination | partial | full |
| Media resistance | very good, with gaps | near-universal |
| Temperature | up to approx. +225 °C | up to approx. +340 °C |
| Price level | medium | high |
| Typical use | Industry, standard | Chemicals, pharma, semiconductors |
FKM covers a large part of industrial applications economically. FFKM is the choice when temperature and media reach the limit. More on this in the article FKM O-rings.
FFKM, ECOLAST and Kalrez: material and brands
FFKM is the material designation. Alongside it there are several brand names for perfluoro-rubber from different manufacturers:
- ECOLAST® is our own FFKM brand (NH O-RING)
- Kalrez® is the FFKM brand from DuPont
- Simriz® comes from Freudenberg
- Chemraz® comes from Greene Tweed
For many years Kalrez was the best-known FFKM brand. Today, high-performance alternatives are available. With ECOLAST you get FFKM O-rings in European brand quality, in over 5,000 sizes available from stock and with no minimum order quantities.
ECOLAST guidance for other designations
Do you have an enquiry with the compound designation of another manufacturer? The following overview lists ECOLAST compounds with a similar application focus and serves solely as a non-binding first orientation for the conversation with us.
Please note: this overview is expressly not a statement about equivalence, interchangeability, identical properties or approvals, and not a recommendation to replace any particular product. Kalrez®, Chemraz®, Perlast® and Isolast® are trademarks of their respective owners. NH O-RING has no business relationship with these companies and names the designations solely to identify an enquiry. Only the relevant ECOLAST data sheet is authoritative; suitability must be checked separately for each application.
| ECOLAST (NH O-RING) | Kalrez® | Chemraz® | Perlast® | Isolast® |
|---|---|---|---|---|
| NH4700 | 6221 | n/a | G74S | J9516 |
| NH5700 | 6230 | n/a | G70A | J9515 |
| NH5750 | 6375 | 505, 605 | G80A | J9503 |
| NH5751 HT | 4079 | 615, 555 | G75B | J8325 |
| NH5755 HT | 1050 LF | 551 | n/a | n/a |
| NH5756 HT | 7075 | n/a | n/a | n/a |
| NH5760 LT | 0040 | n/a | G75LT | n/a |
| NH5901 HT | 7090 | 600 | G90A | J9512 |
Information provided without guarantee. The third-party designations listed only help to match an existing enquiry to a suitable ECOLAST compound for further clarification.
ECOLAST: our FFKM compounds
FFKM does not come in just one version. Through its composition, the temperature range, hardness and approvals can be tailored specifically. Our ECOLAST range covers the common requirement profiles:
| Compound | Temperature | Hardness | Profile / approval |
|---|---|---|---|
| NH4700 (white) | −20/+270 °C | 70 Shore A | FDA, USP Class VI, 3-A |
| NH7700 (white) | −20/+270 °C | 70 Shore A | FDA, USP Class VI |
| NH5750 | −25/+270 °C | 75 Shore A | Standard, FDA |
| NH7750 | −25/+270 °C | 75 Shore A | Standard |
| NH5751 HT | −15/+330 °C | 75 Shore A | High temperature |
| NH7751 HT | −15/+330 °C | 75 Shore A | High temperature |
| NH5755 HT | −15/+330 °C | 75 Shore A | Steam and hot water |
| NH5756 HT | −15/+340 °C | 75 Shore A | High temperature +340 |
| NH5760 LT | −40/+270 °C | 75 Shore A | Low temperature −40 |
| NH5901 HT | −15/+320 °C | 90 Shore A | Oil and gas, high pressure |
The white compounds NH4700 and NH7700 are designed for food, pharma and hygiene applications. You will find all test values on the ECOLAST page and in the data sheets.
Technical properties at a glance
The following values come from the ECOLAST data sheets and are tested to ASTM. The hardness is given as a rounded nominal value, and the compression set applies for 70 h at 200 °C.
| Compound | Hardness Shore A | Tensile strength MPa | Elongation at break % | CS % | TR-10 °C |
|---|---|---|---|---|---|
| NH4700 | 70 | 13 | 130 | 24 | −2 |
| NH7700 | 70 | 12.5 | 135 | 23 | −2 |
| NH5750 | 75 | 18 | 145 | 18.5 | −4 |
| NH7750 | 75 | 17 | 155 | 18 | −4 |
| NH5751 HT | 75 | 17.8 | 152 | 19.5 | −4 |
| NH7751 HT | 75 | 17 | 165 | 18.5 | −4 |
| NH5755 HT | 75 | 16.4 | 155 | 20 | −4 |
| NH5756 HT | 75 | 10.3 | 140 | 14 | −1 |
| NH5760 LT | 75 | 16.7 | 257 | 30 | −30 |
| NH5901 HT | 90 | 20.6 | 110 | 18 | −4 |
CS = compression set (70 h / 200 °C). Tensile strength and elongation at break to ASTM D412, compression set to ASTM D395 B (70 h / 200 °C), TR-10 to ASTM D1329, hardness to ASTM D2240. Manufacturing-related variations possible; the relevant data sheet is authoritative.
What is an FFKM compound made of?
An FFKM compound is more than the base polymer. Only the interplay of several components determines the temperature range, hardness, approval and compression set:
- Base polymer (perfluoroelastomer): the fully fluorinated rubber. It provides the near-universal chemical resistance.
- Cross-linking system: largely determines the upper temperature limit and the compression set. Special cross-linkers enable the high-temperature types up to +330 °C or +340 °C.
- Fillers: reinforce the mechanical properties. The black types use carbon black, while the white food and pharma types NH4700 and NH7700 rely on light, food-compliant fillers. This also explains the higher density of 2.41 g/cm³ compared with 1.98 g/cm³ for the black standard types.
- Pigments: determine the colour, for example white for visual inspection in food production.
The exact formulation and the polymer content per compound are manufacturer-specific and are disclosed on request. We are happy to clarify directly with you which compound suits your application.
| Component | Function | typical phr | approx. wt.-% |
|---|---|---|---|
| FFKM base polymer (terpolymer of TFE, PMVE and cure-site monomer) | fully fluorinated backbone, provides the universal resistance | 100 | approx. 80 to 85 % |
| Filler (carbon black in black types, light or mineral fillers for high purity) | reinforcement, sets the hardness | 10 to 20 | approx. 12 to 18 % |
| Cross-linker system (peroxide with coagent TAIC, or triazine via nitrile cure sites) | forms the thermally very stable network | 2 to 5 | approx. 2 to 4 % |
Typical guide values for a black standard FFKM compound. FFKM does not need bisphenol acid scavengers like FKM. In our black ECOLAST compounds, the organic content is around 80 to 84 % according to TGA per ISO 11358-1, and the carbon black content is about 15 %. High-purity semiconductor and pharma types are run with special, often fully fluorinated fillers or entirely filler-free to avoid particles and metal ions. Specific formulations are manufacturer-specific.
Typical applications
Design and installation
You design FFKM O-rings essentially the same way as other elastomers. Determine groove dimensions and tolerances conveniently with the O-ring groove calculation and the O-ring tolerances. Because FFKM barely swells, the compression can tend to be set somewhat lower. Practically any oil or grease is suitable as an assembly lubricant, since FFKM is resistant to oils and greases.
Are there alternatives to FFKM?
When media resistance matters most and full elasticity does not, FEP-encapsulated O-rings and PTFE O-rings are a more economical option. Both are also near-universally resistant. Important: these materials are considerably more rigid. The installation space must be designed accordingly; FEP is suitable only as a flange and rod seal, PTFE exclusively as a flange seal.
Frequently asked questions
What does FFKM mean?
What is the difference between FFKM and FFPM?
What is the difference between FFKM and FKM?
What is the difference between FFKM and Kalrez?
What temperature range do FFKM O-rings cover?
Why are FFKM O-rings so expensive?
How long can FFKM O-rings be stored?
