Simriz® O-Rings

What Simriz is

Freudenberg describes Simriz as a perfluoroelastomer family with the chemical stability of PTFE and the elastic recovery of a rubber, made on its own patented cross-linking system. The maker contrasts two cure systems in its brochure: a peroxide cure that serves to about 230 C and a triazine cure that carries the high-temperature grades past 300 C. The line splits into a general grade, a low-temperature grade, a white grade, a food grade, an acid and steam grade, a decompression grade and three aerospace grades.

The nine grades on file

The figures below are the maker's, read from the brochure table, sorted by the maker's maximum figure rather than by the brochure's sequence, with each grade's purpose in our words. Freudenberg publishes them as typical values for the compound, not as specification limits for a part. A grade the brochure names without figures is listed by name only.

Simriz 498 is rated by its maker from -6 C to 325 C and is the grade for dry heat, and Simriz 501 shares that -6 C to 325 C range on the aerospace list. Simriz 481 is rated from -30 C to 230 C and is the cold grade, while Simriz 485 is rated from -7 C to 230 C and is the maker's general grade. Simriz 134 is rated from -15 C to 230 C at 90 Shore A for decompression service.

The aerospace grades and AMS 7257

AMS 7257 is the SAE document for perfluorocarbon rubber sealing rings in aerospace fluid systems, and a part to it must come from a compound on the document's qualified products list. Freudenberg's brochure lists Simriz 501 and Z7257 on that list, states that Simriz 498 and Z7257 meet the AMS 7257 specifications, and names jet-engine and auxiliary-power-unit service and two turbine oils for them. A print that calls out AMS 7257 is asking for a QPL-listed grade with the maker's certificate, and Conquest passes that certificate through with the part.

The white, food and semiconductor grades

Simriz 486 is the white grade: no carbon black, so nothing dark sheds into a product stream, and the maker lists it as FDA compliant. Simriz 484 is the food and pharmaceutical grade, listed by the maker to the 3-A sanitary standard, FDA and USP Class VI. Both listings are the maker's and ship as the maker's documents. Freudenberg also names Simriz 508 and 508CP for semiconductor wet processing and plasma on its web pages, but no sheet for them is retained here, so this page states no figure for them.

Simriz on a print that names another brand

Aerospace and chemical-process prints often name Kalrez® or Chemraz® with an "or equal". Simriz grades fall into the same families, and the brands and grades cross-reference puts the maker figures side by side so the comparison starts from sheets. Whether a Simriz grade may replace the named one is your engineering's decision; Conquest quotes the equal you approve and never decides equivalence for you.

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: FFKM Simriz, High Performance Material in Extreme Conditions, brochure 71 US 011, Freudenberg-NOK Sealing Technologies, read 2026-09-14; Freudenberg Sealing Technologies, FFKM Simriz material page (508 and 508CP named), read 2026-09-14; Parker O-Ring Handbook ORD 5700, section 2.2.10 (read 2026-09-14); SAE AMS 7257 (document named, not reproduced).

Parker is a trademark of Parker Hannifin Corporation. Simriz is a trademark of Carl Freudenberg KG (Freudenberg Sealing Technologies); Kalrez is a trademark of Qnity Electronics; Chemraz is a trademark of Greene Tweed. 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.