PTFE (Teflon®) O-Rings

PTFE is the most misunderstood product we sell, and the confusion always starts the same way: it is listed alongside the rubbers, so people assume it behaves like one. It does not. Every other compound in this handbook is an elastomer, a cured rubber you squeeze into a gland that pushes back for years. PTFE (polytetrafluoroethylene, best known by the Chemours trademark Teflon®) is a thermoplastic with effectively no elastic memory. Compress it and it stays compressed.

What you get in exchange is chemistry almost nothing else can touch. PTFE is fully fluorinated: a carbon backbone wrapped in a dense sheath of fluorine, held by the strongest single bond in organic chemistry. Reagents cannot reach the backbone, so they cannot attack it. Acids, bases, solvents, steam, fuels, oils, all of it runs off.

So the framing for this whole page: PTFE is the answer when chemistry beats every elastomer, and the wrong answer when you need a seal that springs back. Get it backwards and you will chase a leak forever.

Quick specs

Common names

All of these mean the same base material:

• PTFE, the ASTM D1418 material abbreviation
• Polytetrafluoroethylene, the full polymer name
• Teflon®, the Chemours trademark that became the generic word for it
• Virgin PTFE, meaning unfilled base resin with nothing blended in

Mechanical properties

Read this list as a plastic’s property set, not a rubber’s:

• Rigid, not resilient. It deforms under load and holds the deformation.
• The lowest friction of any common seal material, and naturally non-stick.
• Dimensionally stable. It does not swell in media the way an elastomer does.
• Does not age. No ozone cracking, no weathering, no UV attack, no shelf-life clock.
• Excellent electrical insulator.
• Useful at cryogenic temperatures, where rubber has long since turned to glass.
• Poor creep resistance. Under sustained load it cold flows, and that one property governs every design decision around it.

Limitations

This is the heart of the page. None of these are surprises once you accept that PTFE is a plastic:

• No elastic memory. A PTFE O-Ring takes a permanent set the first time you compress it. It seals by being squeezed into place, not by springing back. Relax the load and it will not chase the gap.
• Cold flow and creep. Under sustained load PTFE slowly flows out from under the pressure. Bolt loads relax, the seal thins, and leakage can show up months after a good installation. Both effects worsen as temperature and load rise.
• It needs more closing force. There is no soft rubber to conform for you, so flanges need real bolt load and hardware that carries it without deflecting.
• It will not tolerate a rough or scratched sealing surface. Rubber flows into a light scratch and seals over it. PTFE will not. It wants a smooth, well-finished gland.
• Not a dynamic O-Ring material. In a reciprocating or rotating gland the low friction does not save it: with no recovery to follow runout or wear, it wears the gap open and leaks. Dynamic PTFE sealing belongs to spring-energized and jacketed designs, not a solid ring.
• Installation is unforgiving. It does not stretch. A PTFE O-Ring yanked over a shoulder is usually a scarred O-Ring. It commonly needs to be warmed first, or it needs a split or dovetail gland so it never has to stretch at all. See Installation, the installation damage failure mode, and Groove Design before you cut hardware.

Two escape hatches, said plainly:

• If you want PTFE chemistry WITH elastomer recovery, that is exactly what PTFE Encapsulated O-Rings are for: an elastomer core doing the springing, inside a seamless PTFE jacket doing the chemistry.
• If you want an elastomer that approaches PTFE chemistry, that is FFKM: a true rubber with near-universal resistance, priced accordingly.

Chemical compatibility

Handles well:

• Strong acids, including nitric and sulfuric
• Strong bases and caustics
• Solvents of essentially every family: ketones, esters, ethers, amines, chlorinated and aromatic hydrocarbons
• Steam, hot water, fuels, crude oil, petroleum oils, greases, and hydraulic fluids
• Oxidizers, ozone, weather, and UV
• In short, effectively the entire compatibility chart, which is why PTFE is the fallback when everything else rates poor

Attacks it:

The list is short, unusual, and worth knowing exactly:

• Molten alkali metals (sodium, potassium) and their solutions
• Elemental fluorine and some fluorinating agents, especially at temperature
• Chlorine trifluoride

That is close to the whole list. Everything else is a mechanical question rather than a chemical one. Confirm your media on the Chemical Compatibility page or the interactive Chemical Compatibility Chart. If PTFE is the only material that clears your fluid, the real design work is the gland, not the chemistry.

A word on temperature ranges

Our published range is -100°F to +500°F (-73°C to +260°C), an exceptional span: roughly 600 degrees, wider than any elastomer in this handbook. But read it correctly.

PTFE’s practical limit is usually mechanical, not chemical. The polymer is still chemically indifferent at the top of the range. What gives out is its ability to hold a load. Creep and cold flow accelerate with both temperature and stress, so a joint that is fine at +200°F can relax steadily at +450°F under the same bolt load. Toward the top PTFE begins to lose mechanical integrity outright, and the useful question stops being “will the media attack it” and becomes “will it stay where I put it.”

At the cold end it is one of the few materials genuinely useful at cryogenic temperatures, because it has no rubbery state to fall out of. It was never resilient, so it has nothing to lose.

As with every material here, a published range assumes the compound, the media, the pressure, the hardware, and the duty cycle all cooperate. Heat plus sustained load shortens PTFE life faster than heat alone. If your application sits near an edge, send us the conditions.

Shop PTFE O-Rings

Inch (AS568):

• PTFE AS568 O-Rings (Teflon®)

Metric:

• PTFE Metric O-Rings

We also stock PTFE back-up rings. If you need a filled grade or a special size, ask us.

Variations and grades explained

Because PTFE is a thermoplastic rather than a cured rubber, the grades come from what is blended into the resin, not from durometer or cure system.

• Virgin PTFE: unfilled base resin, white to translucent. The purest chemistry, the lowest friction, and the standard for chemical and FDA service. It is also the weakest on creep, which is the trade.
• Filled grades: a filler compounded into the resin to improve creep resistance, load capacity, and wear. You buy that with reduced chemical resistance and reduced purity, since the media now sees the filler as well as the polymer.
  • Glass-filled: the common choice. Better stiffness and creep resistance under load, but avoid it in hydrofluoric acid and strong caustics, which attack the glass.
  • Carbon- or graphite-filled: better wear and thermal conductivity, graphite adding lubricity.
  • Bronze-filled: the highest load and pressure capacity. Not for clean or chemical service.
• Modified PTFE: a small comonomer addition that improves cold-flow behavior while keeping virgin-grade chemistry. Useful when creep is the problem but purity cannot move.
• PTFE back-up rings: a major reason we stock PTFE at all, and we stock them in AS568 sizes. A back-up ring does not seal. It sits in the gland downstream of an elastomer O-Ring and closes the extrusion gap so the soft seal cannot be pushed into it under pressure. PTFE’s rigidity, the very thing that disqualifies it as a plain O-Ring, is what makes it right here. See Back-Up Rings for solid, split, and spiral types.
• PTFE-encapsulated O-Rings: PTFE jacket, elastomer core. This chemistry with real recovery. See PTFE Encapsulated.
• FDA grades: virgin PTFE is routinely supplied for food, beverage, and pharmaceutical contact. See FDA 21 CFR.
• USP Class VI grades: available for medical and biopharma service. See USP Class VI.

Standards and specifications

PTFE O-Rings ship in the AS568 inch range and common metric sizes. Because PTFE is not a rubber, the ASTM D2000 line-callout system that governs elastomer purchasing does not apply. What you will actually see:

• ASTM D1418 lists PTFE among its material abbreviations, even though the standard itself is a rubber nomenclature document.
• ASTM D1710, commonly referenced for PTFE rod, tube, and basic shapes.
• ASTM D4894 / D4895, commonly referenced for PTFE molding and extrusion resins.
• FDA 21 CFR for food-contact service. See FDA compliance.

If your drawing calls out a grade, filler, or resin spec, tell us and we will match it, 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, or Design & Engineering for the gland around the seal.

Is PTFE the right choice?

Three questions settle it:

1. Is chemistry the whole problem? If your media wipes out every elastomer in the materials list, PTFE is very likely the answer, and nothing else is close.
2. Does the seal need to spring back? If it does, PTFE is the wrong answer, full stop. Go to PTFE Encapsulated for the chemistry with recovery, or FFKM for a true elastomer that gets most of the way there.
3. Can your hardware carry the load? Smooth finish, real closing force, a gland that respects cold flow. Give PTFE a worn flange and light bolts and it will leak, and that will not be the material’s fault.

One more, separate from all of that: if you are here because an elastomer O-Ring is extruding under pressure, you do not want a PTFE O-Ring. You want a PTFE back-up ring behind the elastomer you already have.

Not sure whether PTFE, an encapsulated O-Ring, or FFKM is the right call? Send us the conditions: the media, the temperature, the pressure, whether the seal moves, and what the hardware looks like. We will spec it with you, and we will tell you when a cheaper material already does the job. We make getting O-Rings easy.

PTFE appears among the material abbreviations in the Freudenberg FST 2025 Technical Manual, ch. 2, §12, Tab. 12, p. 180, though it is listed there as a thermoplastic rather than an elastomer. Property data, temperature range, and chemical resistance reflect the wider PTFE market. The datasheet for your specific grade always governs; test parts in your actual service conditions before committing to a critical seal.