FFKM O-Rings

What FFKM is, and how it differs from FKM

A perfluoroelastomer is built from tetrafluoroethylene, a perfluorinated vinyl ether and a small amount of a cure-site monomer. Every position on the polymer chain that would carry a hydrogen atom in an ordinary rubber carries fluorine instead. That is why chemistry that eats FKM, such as ketones, amines, hot steam and strong oxidizers, leaves FFKM largely alone. The price of that inertness is a rubber that is costlier than the other common O-ring families, stiffer in the cold, and made by only a handful of companies.

FKM, the fluoroelastomer family sold as Viton® and its equals, still carries hydrogen on the chain. It serves oils, fuels and most solvents to 204 C on the Parker range and costs far less. FFKM earns its place only where FKM fails on chemistry or heat, which is why the FFKM vs FKM guide starts with the medium, not the temperature.

Why the cure system decides the grade

The cure-site monomer is the part of the recipe that lets the chains cross-link, and the makers use two chemistries. A peroxide cure gives the widest chemical resistance and the better low-temperature flexibility; a triazine cure, formed from a nitrile cure site, gives the highest continuous temperatures and the lowest compression set at heat. Several makers also run proprietary cross-link systems that they describe only in their own literature. The result is that every maker's line splits into the same families, even though the grade numbers differ.

The families are our grouping of the makers' own descriptions, not a rating. The brands and grades cross-reference lists every maker and the grades on file side by side.

The temperature figures on file

Two kinds of figure appear on this site, and they are kept apart. The family figure is the Parker O-Ring Handbook range, the one figure that applies before a grade is named. A grade figure is the maker's own, read from the sheet retained here, and it belongs only to that grade. On the sheets on file, FFKM grades run from -42 C to 327 C, and no grade covers that whole span.

Read across the table and the pattern is plain. Kalrez 7075 is rated by its maker from -18 C to 327 C and Chemraz 615 from -18 C to 324 C, and Qnity's sheet keeps 7075 out of hot water and steam. Kalrez 0040 is rated down to -42 C and Simriz 481 down to -30 C, which is where a general grade like Simriz 485 at -7 C to 230 C stops flexing. A grade's own sheet governs the final choice; the makers publish these as typical values, not specification limits.

Who makes FFKM

Kalrez is the line made by Qnity Electronics, the DuPont electronics spin-off that took the brand with it in November 2025. Chemraz is Greene Tweed's line, with a general grade, a high-temperature grade and an oilfield grade with a published rapid-gas-decompression test record. Simriz comes from Freudenberg Sealing Technologies, whose aerospace grades are listed to AMS 7257 by the maker.

Perlast is made by Precision Polymer Engineering, part of IDEX. Isolast is Trelleborg Sealing Solutions' family, with PureFab grades for semiconductor chambers and XploR grades for oil and gas. Parofluor is Parker Hannifin's FFKM, and Markez® is the line sold by Marco Sealing Solutions. Conquest holds no license from any of them; we supply finished parts and name the maker and grade on every quote.

Where FFKM is specified, and where it is not

FFKM goes into chemical process pumps, valves and reactors that see mixed and changing media; into semiconductor etch, deposition and thermal chambers where a seal must shed almost no particles; into downhole tools and compressors that decompress fast; into pharmaceutical and food equipment cleaned with hot caustic and steam; and into jet engines and auxiliary power units on the aerospace grades. In each case the print usually names the maker and grade, because the families above are not interchangeable.

Every maker also lists what its FFKM does not serve, and the lists agree on three things. Fully fluorinated refrigerants and solvents swell it, molten or gaseous alkali metals attack it, and the cold limit is the grade's own low figure rather than a family number. Thermal expansion is greater than FKM's, so a hot gland needs the room the makers' design notes describe. Cost is the other limit, and the honest test is whether an FKM, an Aflas® or an EPDM already survives the medium.

AMS 7257 and other callouts

AMS 7257 is the SAE document for perfluorocarbon rubber sealing rings in aerospace fluid systems. A print that names it is asking for a compound on that document's qualified products list, molded and certified by a listed maker. Freudenberg lists Simriz 501 and Z7257 to it, and other makers list their own grades. Commercial prints more often name a maker and grade directly, or say FFKM with a hardness; either way, the buyer names the grade to quote.

Food and pharmaceutical prints name FDA compliance, USP Class VI or 3-A; oilfield prints name NORSOK M-710 or ISO 23936-2. Each of those belongs to the maker's grade and ships as the maker's certificate. Conquest passes the certificate through with the part.

How to specify an FFKM O-ring

Send the AS568 dash number or the inside diameter and cross-section, the maker and grade if the print names one, the medium, the temperature and the pressure. If the print says FFKM with an "or equal", say whether your engineering has already approved an equal; Conquest quotes what you approve and does not decide equivalence for you. A cleanroom, a food line or an aircraft pulls the grade from a different family, so name the grade your print or your engineering specifies; the quote names the maker, that grade and its sheet.

Sizes and forms we supply

All 369 AS568 sizes (349 general-purpose dash sizes plus the 20 boss-seal sizes) and the ISO 3601 metric series, in the durometers listed above. The AS568 chart and the metric chart carry the dimensions, and the dash number guide explains the numbering.

Sources: Parker O-Ring Handbook ORD 5700 service temperature table, page 7-2 (read 2026-09-25); Parker O-Ring Handbook ORD 5700, section 2.2.10 (read 2026-09-14); Kalrez Perfluoroelastomer Parts in Chemical Process Industry, Product Selector Guide KZE-A40126, Qnity Electronics (formerly DuPont), November 2022, read 2026-09-14; Kalrez Semiconductor Product Selector Guide KZE-H88232, DuPont, February 2012, read 2026-09-14; Chemraz 505, 615, 526 and 605 product brochures EN-DS069, EN-DS081, EN-DS011, EN-DS080, Greene Tweed, 2018, read 2026-09-14; FFKM Simriz brochure 71 US 011, Freudenberg-NOK Sealing Technologies, read 2026-09-14; Perlast G75B datasheet, Issue 4, Precision Polymer Engineering, read 2026-09-14; Advanced Isolast Capabilities brochure, Trelleborg Sealing Solutions, 2021, read 2026-09-14; Parofluor FF350-75 datasheet, Parker O-Ring Division, October 2003, read 2026-09-14; ASTM D1418; SAE AMS 7257 (documents named, not reproduced).

Parker is a trademark of Parker Hannifin Corporation. Kalrez is a trademark of an affiliate of Qnity Electronics, Inc.; Chemraz is a trademark of Greene, Tweed Technologies, Inc.; Simriz is a trademark of Carl Freudenberg KG (Freudenberg Sealing Technologies); Perlast is a trademark of Precision Polymer Engineering Limited; Isolast is a trademark of Trelleborg Sealing Solutions UK Ltd; PureFab is a trademark of Trelleborg Sealing Solutions Germany GmbH; XploR is a trademark of Trelleborg Group; Parofluor is a trademark of its owner; Markez is a trademark of Marco Rubber & Plastics, LLC (Marco Sealing Solutions); Viton is a trademark of The Chemours Company FC, LLC; Aflas is a trademark of AGC Inc. No affiliation or endorsement is implied.

Reviewed by Grant Midstokke, Conquest Seal Corporation. Last updated September 2026. Material ranges are the published references named beside them; the compound datasheet and your application govern the final choice.