In fact FKM does not have any serious disadvantages.
Of course, the FFKM is superior to the FKM in every respect, but the FKM is significantly cheaper. If no extreme requirements make it necessary to choose an FFKM O-ring, then an FKM O-ring is an excellent alternative.
A small minus point is that the cold flexibility is rather low compared to other O-ring materials. However, FKM is available in LT compounds (LT = low-temperature) that are resistant down to -40°C.
Otherwise, a real classic is the confusion regarding the ISO designation. To help you avoid falling into this trap in future, we have briefly explained the term:
FKM is currently the official name for fluororubber.
FPM is an obsolete term for fluororubber.
VITON is FKM and only a trademark of the DuPont company.
Summary of the disadvantages
– FKM has hardly any serious disadvantages
– Low flexibility at low temperatures
– Comprehension problems with the designation (FKM, FPM, VITON)