| Property | FKM | FFKM |
|---|---|---|
| Max continuous temperature | +200°C | +275–327°C (compound dependent) |
| Resistance to most chemicals | Very broad | Near-universal |
| Ketones (acetone, MEK) | Poor — FKM fails here | Excellent |
| Strong amines / caustics | Poor | Excellent |
| Strong acids (concentrated) | Fair | Excellent |
| Steam (high pressure/temp) | Poor | Good–Excellent |
| Semiconductor process chemicals | Not suitable | Standard specification |
| Cost vs NBR | 3–8× NBR | 50–200× NBR |
| Availability | Stock | Longer lead time |
FFKM (also called perfluoroelastomer — marketed as Kalrez by DuPont and Chemraz by Greene Tweed) is specified when FKM has been confirmed to fail chemically, or when continuous service temperature exceeds 200°C. Confirm the failure mode on a known failed FKM O-Ring before specifying FFKM — the cost difference is significant. FITCO can supply FFKM as a Kalrez alternative at competitive pricing from India.
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