PFAS Restrictions and FKM Seals: What Buyers Should Review Before Changing Materials

A practical guide to regulatory status, chemical resistance, qualification testing and supply continuity for fluorocarbon O-rings

The Restriction Is Moving Forward, but It Is Not a Finished Ban

PFAS-related‍‌‍‍‌ discussions are now going well beyond what was a common environmental theme and right into the seal buyer’s email. The European Chemicals Agency put out the revised proposal for EU-wide restrictions under REACH in August 2025 and that included sealing as one out of eight additional sectors which were assessed only after reviewing more than 5,600 consultation comments. The revised proposal also considered various other options besides full immediate ban such as continued use under defined conditions where risks can be ‍‌‍‍‌controlled.

The process advanced again in 2026. ECHA's Risk Assessment Committee adopted its opinion in March, while the Socio-Economic Analysis Committee agreed a draft opinion and opened a consultation that closed on 25 May. The restriction still has to complete the EU decision-making process. As of August 2026, buyers should not describe PFAS restrictions as a final blanket ban on every fluorinated seal sold into Europe.

The unfinished legal process does not make waiting a good plan. Product declarations, customer questionnaires and requests for alternative materials are already appearing. Companies using FKM seals now have a useful window to identify where the material is essential, where another elastomer could work, and which applications would need long qualification programmes.

Why FKM Is Part of the Conversation

FKM is the ASTM and ISO family designation commonly used for fluorocarbon rubber. The polymer is valued because carbon-fluorine chemistry can provide strong resistance to heat, fuel, oil and many aggressive fluids. The fluorinated polymer structure places FKM seals inside the broader regulatory discussion around PFAS, even though a cured O-ring is very different from a mobile processing chemical or a surfactant in water.

The practical job is identification. Buyers need to know the compound family, the finished part number, the manufacturing location, the market where the part will be sold and the declaration requested by the customer. PFAS restrictions can also interact with existing limits for particular PFAS subgroups and impurities, so a one-line statement such as 'contains FKM' does not answer every compliance question.

Why Engineers Selected FKM in the First Place

The‍‌‍‍‌ fluorocarbon O-rings find their way into various equipment and devices like fuel systems, hot oil equipment, chemical processing plants, vacuum hardware, and automotive powertrain installations. Usually, fluorocarbon O-rings would be the choice for engineers when NBR, which loses its strength at elevated temperature or swells in aromatic Fuels are concerned. Other characteristics such as low gas permeability and good resistance to ageing can also be significant reasons that influence their ‍‌‍‍‌selection.

FKM is not one compound. Fluorine content, cure system, polymer architecture, filler package and post-cure all change performance. Parker's European O-Ring Handbook lists compound-specific FKM examples with static temperature ranges such as -15°C to 230°C, while several high-performance grades are listed to 250°C or 260°C. The compound-specific figures show the range within the family and do not provide a universal rating for every black FKM seal.

There are limits too. Standard grades may perform poorly in hot water, steam, certain amines, ketones or low-molecular-weight organic acids. Low-temperature flexibility can be weaker than with some non-fluorinated elastomers. A purchasing rule that simply replaces all fluorocarbon O-rings with one alternative ignores the reason each compound was approved.

For chemical resistant seals, the real specification should name the fluid, concentration, temperature, exposure time, pressure and motion. The polymer name is only the beginning of rubber material selection.

A NASA Replacement Programme Shows the Work Involved

NASA published a useful case after production of an O-ring used with hypergolic propellants was discontinued because a key compound ingredient was no longer available. The original part could not simply be replaced with another elastomer of similar hardness. NASA's Engineering and Safety Center worked with O-ring and material manufacturers and carried out short- and long-duration compatibility testing.

The lesson applies directly to PFAS restrictions. A supplier declaration can identify a regulatory issue, but it cannot prove seal performance. Changing from FKM seals to another compound can alter swelling, compression set, friction, permeability and low-temperature recovery. The same rule applies to fluorocarbon O-rings. A replacement is complete only after the relevant risks have been tested and the drawing, specification and approval records have been updated.

The Main Alternatives Have Different Strengths

NBR remains a practical choice for many mineral oils and moderate-temperature hydraulic systems. HNBR generally offers better heat, ozone and mechanical performance than standard NBR. EPDM is widely used with water, steam, brake fluids and outdoor exposure, but it is normally a poor choice for petroleum oils and fuels. Silicone offers excellent low-temperature flexibility and broad temperature capability, although tear and wear resistance can limit dynamic use.

FEPM, FFKM, fluorosilicone and PTFE may solve difficult media or temperature problems, but all four families are also fluorinated materials. Suppliers should not present the fluorinated families as a PFAS-free answer without a precise regulatory review. A non-fluorinated alternative may be possible for one service condition and unrealistic for another. Rubber material selection must therefore start with the actual service condition.

Good rubber material selection starts by separating applications. A static water gasket at 80°C should not follow the same decision as a reciprocating fuel seal at 150°C. The first may have several workable options; the second may require a narrower technical and regulatory path.

Testing the Replacement Against the Real Failure Modes

Testing chemical resistant seals often starts with ASTM D471, which compares the effect of liquids on rubber. ASTM D471 can measure changes in mass, volume, dimensions, hardness, tensile strength and elongation after immersion. ASTM notes that accelerated testing provides comparative data and may not directly predict field performance because service conditions vary.

Compression recovery needs a separate check. ASTM D395-18(2025) covers compression set testing and states that the methods are mainly applicable to static stresses. If the part is dynamic, friction, wear and rapid pressure cycling must be added. Chemical resistant seals used in explosive-gas service may also need rapid gas decompression testing.

Regulatory Data Needs the Same Revision Control as a Drawing

A useful supplier declaration identifies the manufacturer, compound code, part or product family, date, applicable regulation and basis of the statement. The declaration should also state whether the claim concerns intentionally added substances, measured content, specific restricted PFAS groups or the broader proposed definition. 'PFAS-free' without a definition is difficult to audit.

For PFAS restrictions, keep the regulatory file linked to the approved material revision. For chemical resistant seals, the compliance claim and test scope must stay linked as well. When the final legal text, thresholds or derogations change, the company can then identify affected parts without repeating a manual search through years of purchase orders.

Do Not Forget the Groove and the Assembly

Installation and cycling are common failure points for chemical resistant seals during substitution. The immersion report may look acceptable, but the new material can tear across a port during installation or wear at the lip after several thousand cycles. A bench coupon cannot represent groove geometry, shaft finish or side load. Finished-part and assembled-system tests close the validation gap.

What Buyers Should Ask Before Approving a Change

Start with the current part list. Which FKM seals are sold into the EU, which are safety-critical, and which have no qualified second source? Record the operating fluid, temperature, pressure, motion and expected service life for each application. The resulting list becomes the rubber material selection map for the project.

Then define the approval route. Decide whether testing will use standard specimens, finished fluorocarbon O-rings, assembled hardware or all three. Keep the original material as the control wherever possible. A side-by-side result is more useful than comparing a new report with an old catalogue value generated under different conditions.

How Yida Can Support the Material Review

Dalian Yida Precision Rubber Products Co., Ltd. supplies O-rings, gaskets and custom molded rubber components in FKM, NBR, HNBR, EPDM, silicone and other elastomer families. For projects affected by PFAS restrictions, Yida can review the existing drawing, compound requirement and operating conditions before samples are prepared.

The review can separate applications that still require the performance of FKM from those where rubber material selection may support a practical alternative. Agreed requirements can include hardness, dimensions, appearance, fluid ageing, compression set and finished-part testing. Send the drawing, medium, pressure, temperature range, motion, quantity and required declaration for a focused material and sampling proposal.