PTFE Encapsulated O-Rings

PTFE encapsulated O-Rings exist to fix the one thing wrong with plain PTFE. Solid PTFE will shrug off almost any chemical you put in front of it, and then fail to seal properly because it has almost no spring. Squeeze it and it stays squeezed. It cold flows, it takes a set, and it never really pushes back.

An encapsulated O-Ring is a two-part seal. A seamless PTFE jacket, sometimes FEP or PFA instead, completely wraps an elastomer core. The jacket is the only thing the fluid ever touches, so you get PTFE chemistry on every wetted surface. The core, usually FKM (Viton®) or silicone, sits sealed inside and does nothing but push outward. It is a spring in a chemical-proof coat.

That single sentence explains the entire product. The jacket sets the chemistry. The core sets the temperature. It also explains the limitations, because a solid fluoropolymer skin does not behave like rubber no matter what is underneath it.

Quick specs

Common names

The same part gets called a lot of things on drawings and in purchasing systems. All of these mean the same construction:

• PTFE encapsulated O-Ring, the general term
• Teflon® encapsulated, using the DuPont trade name for the fluoropolymer family
• FEP encapsulated or PFA encapsulated, naming the specific jacket resin
• Jacketed or encapsulated O-Ring
• Often specified as a pair, such as FEP jacket / silicone core

Mechanical properties

• Near-universal chemical resistance on every wetted surface, because the media only ever sees fluoropolymer
• Elastic recovery from the core, which is the whole reason the part exists
• Very low friction and a non-stick jacket surface, so media does not cling to the seal
• Very low permeability, and no plasticizers or extractables to leach into the process fluid
• Effectively unlimited shelf life; the jacket does not age, oxidize, or weather
• Handles a wider chemical range than any single elastomer, including compounds that would destroy FKM or EPDM outright

Limitations

This is the honest list, and on this product it is the most important section on the page. An encapsulated O-Ring is a compromise, and you need to know which way it compromises.

• Static service only. This is not a dynamic seal. In reciprocating or rotating service the jacket wears through, and the moment it is breached the core is exposed to the very media you bought the jacket to keep out. There is no partial failure here.
• Less squeeze and less recovery than rubber. You are compressing a solid fluoropolymer skin. It takes more closing force to seat, and it is less forgiving of a marginal gland. Get the groove design right rather than hoping the seal absorbs the difference.
• Less forgiving of surface finish. A rubber O-Ring flows into a scratch across the sealing face. This one may not. Flange and gland surfaces need to be genuinely good.
• Installation is unforgiving. The jacket creases, kinks, or splits if the ring is stretched too far or dragged over a sharp edge or a thread. A creased jacket is a leak path, permanently, and it will not relax back out. See Installation and installation damage. These are often warmed slightly before installation to make the jacket more compliant.
• Once the jacket is breached, the seal is done. There is no margin. Damage means replace, not monitor.
• Not for extrusion-prone glands at high pressure without support. The jacket does not resist gap extrusion the way a hard elastomer does. Add back-up rings or close the gap.
• Costs more than a plain elastomer O-Ring. If a standard compound covers your fluid, it covers your fluid, and we will tell you so.
• If you need a true elastomer with near-PTFE chemistry, this is the wrong part. Go to FFKM.

Chemical compatibility

Handles well:

• Strong acids, including oxidizing acids
• Strong bases and caustics
• Ketones, esters, and aldehydes, which wreck most oil-resistant elastomers
• Aromatic and chlorinated solvents
• Amines
• Steam and hot water
• Fuels, oils, and hydraulic fluids of every description
• Ozone, UV, and weather

Attacks it:

The realistic list is very short and mostly exotic: molten alkali metals, elemental fluorine and some fluorinated compounds at temperature and pressure, and a handful of similarly aggressive materials. For ordinary industrial and process chemistry, treat the jacket as inert, exactly as you would treat plain PTFE.

The critical point is that the core’s compatibility does not enter into it, as long as the jacket is intact. The core is never wetted. That is why you can put a silicone core, a material with mediocre chemical resistance on its own, into service against solvents that would swell it to twice its size in an hour. Confirm your fluid on the Chemical Compatibility page or in the interactive Chemical Compatibility Chart.

A word on temperature ranges

Our published ranges are -10°F to +300°F for an FKM core and -80°F to +500°F for a silicone core. Note what changed between those two numbers and what did not: the jacket is the same, the chemical resistance is the same, and the entire difference is the core.

The core sets the temperature range. The jacket sets the chemistry.

That makes the choice of core a temperature and resilience decision, not a chemical one. It is the opposite of how you pick every other O-Ring material on this site, and it is where most people get tangled up.

We stock three cores:

Any published range assumes the compound, the media, the pressure, the hardware, and the duty cycle all cooperate. Sitting at +500°F continuously is not the same duty as touching it. If you are near an edge, send us the conditions.

Shop PTFE Encapsulated O-Rings

Every PTFE encapsulated variation we stock, by size:

Inch (AS568):

• Teflon® Encapsulated (Silicone, Viton® and EPDM cores)

Metric:

• Teflon® Encapsulated Metric

Need a jacket, core, or size that is not listed? Ask us. Much of the encapsulated world is built to order, and we quote it regularly.

Variations and grades explained

An encapsulated O-Ring is two independent choices. Make them separately.

By jacket

All three jacket resins are fluoropolymers and all three give effectively the same broad, PTFE-like chemical resistance. They differ in how they form and how much heat they take.

• PTFE, the standard and most common jacket. The reference point for chemical resistance.
• FEP (fluorinated ethylene propylene), easy to form into a smooth seamless envelope, which makes for a consistent jacket. The most common choice where the jacket needs to be drawn tight over the core.
• PFA (perfluoroalkoxy), buys additional heat capability over FEP with the same chemical resistance, and is the usual pick when the service temperature is pushing the jacket rather than the core.

By core

Covered above, and worth repeating because it is the decision people get backwards:

• FKM (Viton®) core: -10°F to +300°F, more resilient, better under pressure.
• Silicone core: -80°F to +500°F, the wider range, softer.

You are choosing a spring, not a chemical barrier. See FKM (Viton®) and Silicone for what each material is like on its own.

By certification

• FDA grades for food and beverage contact; see FDA 21 CFR 177.2600.
• USP Class VI for pharmaceutical and biotech service; see USP Class VI.

By size

Available across the AS568 inch range and in common metric sizes. Cross section matters more here than on a rubber O-Ring, because a very thin cross section leaves very little core to do the springing.

Standards and specifications

• AS568 inch sizes and common metric sizes, the same dimensional standards as any other O-Ring.
• FDA 21 CFR 177.2600 for jacket and core materials in food-contact service.
• USP Class VI for pharmaceutical and medical applications.
• Certificate of Conformance and lot traceability under our ISO 9001:2015 system.

There is no dedicated military O-Ring spec for encapsulated O-Rings. Unlike nitrile, FKM, silicone, fluorosilicone, and EPR, there is no M-number part standard for this construction. It is bought to a customer drawing or by a jacket and core callout, such as PFA jacket, FKM core, AS568-214. See the mil-spec reference for the compounds that do have one.

Typical applications by industry

See O-Rings by Industry for the wider picture, or the full materials list to compare.

Is PTFE Encapsulated the right choice?

Four questions settle it:

1. Is the seal static? If it slides or rotates, stop. The jacket wears through and the core is exposed. Pick a real elastomer, or FFKM.
2. Does any ordinary elastomer cover your chemistry? If nitrile, EPDM, or FKM handles the fluid, buy that instead. This costs more and installs harder for no benefit.
3. Do you need springback that plain PTFE cannot give? That is exactly the gap this fills.
4. Can your budget carry FFKM instead? That is the honest comparison. FFKM is a true elastomer: it seals better, recovers better, tolerates a rough gland, and works dynamically. It also costs far more. For aggressive chemistry in static service, encapsulated is usually the far cheaper answer and does the job. When static is not enough, FFKM is worth what it costs.

Then get the gland and the installation right. This part is far more sensitive to both than a rubber O-Ring, and that is where most encapsulated seals actually fail.

Not sure whether an encapsulated O-Ring is the right call, or which core you need? Send us the conditions: the media, the temperature, the pressure, and whether the seal moves. We will spec the jacket, the core, and the size with you. We make getting O-Rings easy.

Temperature ranges shown are our published values for the constructions we stock. Encapsulated O-Rings are a composite product with no single governing elastomer datasheet or industry material standard, so construction and performance vary by manufacturer. Confirm the build with us before committing to a critical seal, and test parts in your actual service conditions.