Is fluoroelastomer rubber or plastic?

It resists oil like plastic. It flexes like rubber. So is fluoroelastomer a rubber—or a plastic with rubbery behavior?

Fluoroelastomer is a synthetic rubber, not a plastic. It belongs to a class of flexible, high-performance elastomers designed for sealing in harsh environments.

I’ve had many clients ask this when comparing it to PTFE (Teflon®). They’re both fluorinated—but only one stretches and seals under compression. That one is fluoroelastomer.

What is fluoroelastomer made of?

Fluoroelastomer isn’t just rubber—it’s engineered for survival. Its backbone chemistry is what gives it extreme durability against heat, oils, and chemicals.

Fluoroelastomer is made from fluorinated monomers such as vinylidene fluoride (VDF), hexafluoropropylene (HFP), tetrafluoroethylene (TFE), and sometimes perfluoromethylvinyl ether (PMVE).

🧪 Typical FKM Polymer Types

These monomers are polymerized and vulcanized into rubber sheets, O-rings, or custom-molded seals. Once cured, the material becomes a non-melting, elastic sealing compound ready for industrial use.

What makes fluoroelastomer a rubber?

Rubbers, or elastomers, are polymers that can stretch and return to shape. Plastics, on the other hand, tend to be rigid and non-elastic.

Fluoroelastomer (FKM) behaves like a traditional rubber—it’s compressible, flexible, and seals effectively under pressure.

🛠️ Characteristics of Fluoroelastomer Rubber³

We use FKM in applications that require long-term sealing with flexibility—like O-rings, shaft seals, and gaskets⁴. It fits tightly into grooves and holds its shape without permanent deformation.

Why do people confuse fluoroelastomer with plastic?

Because it’s related to PTFE and other fluoroplastics—and because it’s often found in harsh environments where plastics are also used.

Fluoroelastomer and PTFE share similar chemical resistance, but PTFE is a rigid thermoplastic, while FKM is a flexible rubber elastomer.

🔍 Rubber vs Plastic Comparison

If you need something that bends, seals dynamically, and can be molded into rubber shapes—FKM is your answer. If you need a rigid liner or dry-lubricated contact, PTFE makes more sense.

Where does this matter in real applications?

In chemical pumps, fuel injectors, and valve systems, material behavior under load determines sealing success.

Fluoroelastomer seals conform to imperfect surfaces, recover from dynamic motion, and hold pressure. Plastics can’t.

📌 What FKM Can Do That Plastic Can’t

I’ve seen projects where clients tried PTFE washers as gaskets—only to replace them months later with FKM for long-term success.

Does fluoroelastomer have PFAS in it?

Yes—fluoroelastomer contains fluorine-based chemicals that fall under the broad definition of PFAS (per- and polyfluoroalkyl substances).

All fluoroelastomers are considered part of the PFAS family because they contain multiple carbon-fluorine bonds, which are extremely stable and persistent in the environment.

⚠️ What You Should Know

At Julong, we monitor PFAS-related regulations closely. While FKM is not banned, its use may be restricted in the future for food, medical, or drinking water systems in certain countries. For sensitive sectors, we can suggest alternative materials like EPDM or silicone where appropriate.

FKM remains safe and effective for industrial and automotive use. But if your product is subject to PFAS disclosure or sustainability audits, you should confirm the impact of using fluoroelastomer in your system.

Conclusion

Fluoroelastomer is rubber—chemically advanced, but mechanically elastic. It’s not a plastic, and it’s not rigid. It stretches, seals, and survives where other rubbers fail.

Need flexible, chemical-resistant rubber seals?
Contact Julong Rubber or Request a Quote for molded or extruded FKM parts.

Chat with us anytime on WhatsApp: