Comparison guide
Branded vs Generic FFKM: What the Brand Buys You
Kalrez® is one manufacturer's FFKM; Chemraz®, Parofluor® and value-tier lines are the same polymer family. How to read a Kalrez callout, map the grades across brands, and know when an equal is acceptable.
Kalrez is a trademark, not a material class: it is the FFKM (perfluoroelastomer) line made by Qnity, the DuPont electronics spin-off that took the brand in 2025. Chemraz from Greene Tweed, Parofluor from Parker® and several value-tier FFKM lines are the same polymer family under ASTM D1418, and for most chemical-processing service a grade of equivalent temperature and chemical rating performs the same. The brand buys you a documented grade with a long service record; an alternate grade offers the same perfluoroelastomer chemistry. This guide reads a Kalrez callout, maps the grade families across brands, and sets out who decides an equal.
Who makes FFKM, and what does each brand mean?
| Brand | Owner | What it is | How it is sold |
|---|---|---|---|
| Kalrez | Qnity Electronics (formerly DuPont; the brand moved with the November 2025 spin-off, and datasheets may still say DuPont) | The incumbent FFKM specification on most prints | Finished parts only, through authorized distributors |
| Chemraz | Greene Tweed | A brand alternate with its own grade numbering | Finished parts only |
| Parofluor | Parker Hannifin | Parker's FFKM line | Finished parts |
| Simriz® | Freudenberg Sealing Technologies | FFKM; Simriz 498 is rated by its maker to 325 C; grades 501 and Z7257 are QPL-listed to AMS 7257 | Finished parts |
| Isolast® | Trelleborg Sealing Solutions | FFKM for chemical, semiconductor and high-temperature service | Finished parts |
| Markez® | Marco Sealing Solutions | Brand FFKM line with its own grade numbering | Finished parts |
| Perlast® | Precision Polymer Engineering, part of IDEX | Brand FFKM line with its own grade numbering | Finished parts |
| Viton® (for contrast) | Chemours since 2015 | Not FFKM at all: an FKM polymer trademark that any molder can buy as raw gum | Raw polymer to molders |
Two ownership facts matter in conversation. "We need DuPont Viton" is pre-2015 memory; Viton has been a Chemours trademark since then and constrains the polymer source, not the molder. And Kalrez, unlike Viton, is never sold as raw polymer: every Kalrez part is molded by the brand owner.
How do I read a Kalrez callout?
A print typically reads a dash size plus a grade number, for example 2-214 in Kalrez 6375. The size is the standard AS568 dash number (Parker's 2-XXX prefix is the same size); the grade number is the compound. The grade families, in the manufacturers' own descriptions, are laid out below with the Chemraz grade that serves the same family. Cross-brand matchups are distributor practice, not vendor-published equivalence, and the customer's approval governs.
| Service family | Kalrez grade (Qnity) | Chemraz grade (Greene Tweed) | Note from the manufacturers' grade descriptions |
|---|---|---|---|
| General chemical processing | Spectrum™ 6375 | 505 | Broadest chemical resistance; the maker rates grade 6375 for service to 275 C |
| Highest temperature and mechanical strength | 7075 | 615 | Top thermal grades; 7075 is not for steam |
| Steam and hot water; pharmaceutical | 7375, 7390 | 605 | |
| High pressure and rapid gas decompression | 7090 (90 Shore A), 0090 (95 Shore A) | 526 (97 Shore A) | Oilfield completions, sour gas |
| Low temperature | 0040 | check the grade sheet | The maker rates grade 0040 for service down to -42 C |
| Semiconductor plasma and ultra-pure | 8085, 8575, 9100, 9600, 9400 | G57, G20, E38 | Process-qualified grades; substitution needs the fab's approval |
| Carbon-black-free (white) grades | ask the distributor | 514, 517 | Food, pharmaceutical and semiconductor uses |
| High temperature, older general grade | 4079 | none listed | Rated by the maker to 316 C; not for hot water or steam |
What temperature and chemical performance can you expect?
The Parker O-Ring Handbook (ORD 5700) rates the FFKM class for continuous service from -26 C (-15 F) to 320 C (608 F). Individual brand grade sheets publish figures above that ceiling for their highest-temperature grades; those are manufacturer data for that grade alone and the grade sheet governs. Chemically, every brand's general grade resists aromatics, ketones, amines, acids, bases, steam and vacuum, and shares the one recognized FFKM weak spot, fluorinated refrigerants. The FFKM O-rings guide covers the material, and the chemical compatibility guide the media.
When can a generic FFKM be quoted?
| What the print says | Can a different brand be quoted? | What has to be true |
|---|---|---|
| "FFKM" or "perfluoroelastomer", no brand | Yes | The print or your engineering names the service family (general, steam, high temperature, plasma) and durometer |
| "Kalrez or equal" | As an alternate for the print owner to approve | The equal is the print owner's decision; name the grade your engineering approved and it is quoted with the maker's sheet and the cross-reference |
| "Kalrez 6375" with no "or equal" | Only with the customer's written approval | The buyer must agree to the substitution before the order |
| A grade qualified in a semiconductor or pharmaceutical process | Not without requalification | Process qualification is tied to the grade, not the chemistry |
| An aerospace print to AMS 7257 | Any grade qualified to the specification | The QPL listing, not the brand, is the requirement |
| A USP Class VI or FDA 21 CFR 177.2600 requirement | Yes, if the alternate grade carries the same documentation | Compliance belongs to the grade; ask for the report |
Availability in standard sizes is often the real deciding factor: FFKM in a non-stock size is a molded special from whichever brand owner makes it, so a generic already available in the right grade family can be the practical answer when the print allows it.
What does the RFQ need to say?
Five things settle an FFKM quote. The size, as an AS568 dash number or a measured inside diameter and cross-section in millimeters. The grade family, or the exact grade number if the print names one, together with whether "or equal" applies. The service: media and concentration, continuous and peak temperature, pressure, and static or dynamic. The documentation required: a certificate of conformance ships with every order; a USP Class VI report or an AMS 7257 qualification record is a separate document that ships only when the order asks for it.
And the quantity, because a standard size already available in the right grade family and a molded special are different conversations. With those five on the request, the quote carries the grade you named, its brand and the maker's sheet; send it through the quote request form.
Kalrez is a trademark of Qnity Electronics; Chemraz is a trademark of Greene Tweed; Simriz is a trademark of Freudenberg Sealing Technologies; Perlast is a trademark of Precision Polymer Engineering, part of IDEX; Isolast is a trademark of Trelleborg Sealing Solutions; Parofluor is a trademark of Parker Hannifin; Markez is a trademark of Marco Sealing Solutions; Viton is a trademark of The Chemours Company; Parker is a trademark of Parker Hannifin Corporation. No affiliation or endorsement is implied.
Sources
- Parker O-Ring Handbook ORD 5700, service temperature table, page 7-2 (FFKM -26 C to 320 C), read 2026-09-25
- Parker O-Ring Handbook ORD 5700, section 2.2.10 (perfluoroelastomer heat and cold figures), read 2026-09-14
- Kalrez CPI product selector guide KZE-A40126 (Nov 2022), read 2026-09-14
- Kalrez semiconductor product selector guide (Feb 2012), read 2026-09-14
- Chemraz 505, 526, 605 and 615 product brochures (Greene Tweed, 2018), read 2026-09-14
- Simriz FFKM brochure 71 US 011 (Freudenberg), read 2026-09-14
- Advanced Isolast capabilities brochure (Trelleborg, 2021), read 2026-09-14
- Perlast G75B datasheet, Issue 4 (Precision Polymer Engineering), read 2026-09-14
- Parofluor FF350-75 datasheet (Parker Hannifin, October 2003), read 2026-09-14
- SAE Mobilus record for AMS 7257, read 2026-09-06
- 21 CFR 177.2600, USP Class VI, ASTM D1418 and AS568, named as callouts
Reviewed by Grant Midstokke, Conquest Seal Corporation. Last updated September 2026. Spec values in this guide are drawn from the sources listed above; the compound datasheet and your application conditions govern the final choice.
Frequently asked questions
Is Kalrez better than Chemraz?
They are competing FFKM lines with parallel grade families. In general chemical service the two general-purpose grades perform comparably; in a qualified semiconductor or pharmaceutical process the qualified grade is the one to use, whichever brand it is.
Does "Kalrez" on a print mean I cannot quote anything else?
If the print names a grade with no "or equal", that grade is quoted; an alternate is quoted only when the buyer names one, with the cross-reference, and the buyer decides. If the print says "or equal", the equal is the print owner's decision: name the grade your engineering approved and it is quoted with the maker's sheet.
Who owns Kalrez now?
Qnity Electronics, DuPont's electronics spin-off, since November 2025. Datasheets printed before the transition still carry the DuPont name.
Is Viton a kind of FFKM?
No. Viton is Chemours' FKM (fluoroelastomer) trademark. FFKM is the fully fluorinated perfluoroelastomer family; see the FFKM vs FKM comparison.
What hardness do FFKM O-rings come in?
Conquest's former compound chart lists perfluoroelastomer compounds at 70, 75 and 90 Shore A; on the Parker handbook range the family runs -26 C to 320 C, and named grades reach 327 C on their makers' sheets. Most chemical-processing prints call for 75 A; 90 A is for high pressure or wide clearance.
Is there an aerospace specification for perfluoroelastomer?
Yes, SAE AMS7257 covers 70 to 80 Shore A perfluoroelastomer sealing rings. A print that cites it wants a compound qualified to that document, and the certificate names the manufacturer; a brand name alone does not satisfy it.
Does the brand change the groove or the squeeze?
No. A Kalrez ring and a generic FFKM ring of the same size take the same gland, and the published squeeze bands apply by seal type and cross-section, not by brand. What differs between compounds is swell and thermal expansion, which is what the free volume in the groove is for, so keep the gland fill inside the 60 to 85 percent band (Parker) with 75 percent as the target.
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