O-rings
PTFE-encapsulated O-rings
A PTFE-encapsulated O-ring is an elastomer core, usually silicone or FKM, sealed inside a thin, seamless jacket of FEP or PFA fluoropolymer, the resins sold as Teflon® by Chemours. The jacket gives the ring the chemical inertness of PTFE; the core gives it the recovery that a solid PTFE ring lacks. It is the usual answer where a rubber O-ring fails on chemistry but a solid PTFE ring cannot hold a seal, in static and slow-moving glands such as process flanges, couplings and sanitary fittings.
- Jacket
- FEP or PFATeflon resins by Chemours; other makers' equivalents
- Core
- Silicone or FKMsolid or hollow silicone; FKM for oils and fuels
- Jacket limits
- 200 C / 260 CFEP upper service (UL 746) / PFA continuous use, resin maker's sheets
- Service
- Static, slownot a dynamic seal
What the jacket does, and what the core does
The jacket is a thin sleeve of melt-processable fluoropolymer, FEP or PFA, that the maker forms around the core so no seam faces the medium. It carries the chemical resistance: acids, bases, solvents, oxidizers and cleaning chemistry touch fluoropolymer, not rubber. The core does the pushing back. Squeezed in the groove, the silicone or FKM inside keeps loading the jacket against the mating surfaces, which is the recovery a solid PTFE ring never has.
Because the jacket does not stretch the way rubber does, an encapsulated ring is stiffer than the same size in plain rubber. It needs a groove that respects that: the maker's groove tables, a lead-in chamfer, and a mating finish smoother than a rubber O-ring tolerates. The gland facts already on the size pages, recorded from ERIKS' published guidance on 2026-09-06, put the mating surface for encapsulated rings near 20 microinch Ra.
FEP or PFA
Both jackets come from the same resin family and behave the same way in a groove; the difference is heat and price. The Chemours sheet for Teflon FEP states an upper service temperature of 200 C, and the Teflon PFA properties handbook states a continuous use temperature of 260 C. PFA also holds its shape better at heat, which matters in a jacket only a few thousandths thick. FEP is the usual jacket where the temperature allows; PFA is named when the process runs hotter or the print says so.
| Jacket resin | Figure on the resin sheet | What it is | Usual reason to choose it |
|---|---|---|---|
| FEP | 200 C upper service temperature (UL 746) | Fluorinated ethylene propylene | The standard jacket; lower cost |
| PFA | 260 C continuous use temperature | Perfluoroalkoxy | Hotter service; better shape retention at heat |
Resin figures, not finished-ring ratings: the ring runs at the lower of the jacket figure and the core's family figure, and the ring maker's sheet governs.
Solid core, hollow core, FKM core
A solid silicone core is the common build and the one most sizes ship in. A hollow silicone core compresses with less force, so it seats in glands that cannot squeeze a solid ring hard, such as light flanges and glass or plastic fittings, and it forgives some misalignment. An FKM (Viton®) core is chosen where the medium could reach the core through a damaged jacket and silicone would swell, or where the print names it; its family figure is the FKM range on the Viton page. Cores of a wound stainless spring exist for cryogenic and vacuum service and are quoted to the print.
Where they win, and where they lose
They win in static and slow-moving glands with chemistry that beats FKM and EPDM, where the budget or the temperature does not call for FFKM: chemical process flanges, cam-and-groove couplings, pump housings, sanitary clamp fittings, filter housings and instrument connections. They lose in dynamic service, because the jacket wears and creases where a rubber ring would simply slide, and in glands cut for rubber that squeeze the jacket past what it will take. Where the seal must move, a spring-energized PTFE seal is the PTFE answer; where the chemistry allows rubber, a rubber O-ring is cheaper and more forgiving.
What to send
The AS568 dash number or the inside diameter and cross-section, the jacket (FEP or PFA), the core (solid silicone, hollow silicone or FKM), the medium, the temperature, and whether the gland moves. Send the groove dimensions or the fitting standard, because the groove decides whether an encapsulated ring seals. The quote names the maker and the build and sends the product sheet.
Related pages
Frequently asked
Is a PTFE-encapsulated O-ring the same as a PTFE O-ring?
No. A solid PTFE O-ring is all fluoropolymer and has almost no recovery; an encapsulated ring is a rubber core inside a fluoropolymer jacket, so it recovers like rubber while the medium touches only fluoropolymer.
What temperature can an encapsulated O-ring take?
The lower of the jacket figure and the core's family figure. The resin maker's sheets put FEP at 200 C upper service and PFA at 260 C continuous use; the silicone and FKM pages carry the core figures, and the ring maker's sheet governs.
Can I use one in a dynamic seal?
Not as a rule. The jacket wears and creases under motion; a spring-energized PTFE seal is built for that job.
Why does it need a special groove?
The jacket does not stretch like rubber, so the ring is stiffer, and a rubber-sized groove either squeezes the jacket too hard or leaves the ring loose. The maker's groove table, a chamfered lead-in and a smooth mating finish are the fix.
Solid or hollow core?
Solid for most glands; hollow where the assembly cannot apply much squeeze, such as light flanges and glass or plastic fittings.
Is Teflon the same as FEP and PFA?
Teflon is the Chemours brand for a family of fluoropolymer resins that includes PTFE, FEP and PFA; the jacket is made from one of the last two, and the sheet says which.
Related guides
Sources
Teflon FEP 100-J product information, Chemours 2019 (upper service temperature 200 C, UL 746), read 2026-09-14; Teflon PFA properties handbook (continuous use temperature 260 C), read 2026-09-14; Silicone and FKM core family figures (Parker® O-Ring Handbook ORD 5700, section 2.2, read 2026-09-14); Mating-surface finish for encapsulated rings (ERIKS, via the gland facts on the size pages; recorded 2026-09-06). Dimensional facts are stated in our own words; no standard's text or table is reproduced.
Teflon is a trademark of The Chemours Company. No affiliation or endorsement is implied.
Viton is a trademark of The Chemours Company. No affiliation or endorsement is implied.
Parker is a trademark of Parker Hannifin Corporation. No affiliation or endorsement is implied.
ERIKS is a trademark of its owner; no affiliation or endorsement is implied.
Send the size, the jacket and the core
The dash number or the inside diameter and cross-section, FEP or PFA, solid or hollow silicone or FKM, the medium and temperature, and the groove or fitting standard. A Conquest representative replies with the quote and the product sheet.
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