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FFKM (also written FFPM) is a perfluoroelastomer: a rubber whose polymer backbone is entirely fluorinated, with no C–H bonds. That is what gives it resistance to almost all organic media and to very high temperatures. FKM contains C–H bonds and therefore has a more limited chemical and temperature range. In practice FFKM is specified where FKM would swell, harden or fail — ketones, esters, amines, strong oxidisers, or sustained service above 200 °C.

No. FFKM is an elastomer, so it has rubber elasticity and can be used for dynamic sealing. PTFE is a semi-crystalline fluoropolymer with no meaningful elastic recovery, so a PTFE seal normally needs a spring-energised or convoluted design. Where temperature, chemical exposure and elastic recovery are all required at once, FFKM is usually the better engineering choice.

Start from the constraint that is hardest to change: temperature. Then narrow by medium, then by motion. Above 300 °C continuous, only OME7505 qualifies. Below −20 °C, only OM7542 qualifies. For static seals in etch and CVD where metal ions matter, OMS7102. For plasma service, OMS70S. For chemical delivery and flow meters, OM7502. For high-pressure gas or extrusion-critical service, OM9090. The grade pages give the full property table for each.

Compression set is the permanent loss of shape an elastomer takes after being held at a defined deflection, temperature and duration — it is the reason a static seal stops sealing. The value is only meaningful alongside the condition it was measured under. A grade tested at 200 °C will perform worse at 300 °C than a grade whose higher reading was measured there. Every grade page on this site states the exact condition used.