FKM, IIR and CR material families

Technical explanation

FKM is the fluoroelastomer family, IIR the butyl rubber family and CR the chloroprene rubber family. These chemical family names do not give the same temperature or chemical resistance limit for every product. In particular, cleaning cycles, gas contact and low-temperature behavior are evaluated product by product. The family columns in chemical charts can be used for preliminary screening; results for different compounds are not directly equated. Seal selection should not be made automatically from the name of the hose inner tube either.

Source: S020, S037

Topic-specific checkpoints

Source: S020, S037

How is it assessed in practice?

Instead of closing an alternative material request with 'make it FKM', write down the problem to be changed: is it swelling, hardening or gas permeation? Ask the supplier for the actual compound code and an assessment for the application conditions. Do not use the color or flexibility of the old seal as a definitive material identification. Also check the assembly dimensions for the new part; a chemically suitable compound does not solve the problem of wrong geometry. Link the response document to the order and revision. Do not treat the FKM, IIR or CR family name as compatibility approval until the actual compound code and service condition have been verified.

Original editorial recommendation; not a clause of a standard.

Frequently asked questions

Is a more expensive elastomer better with every fluid?

No. The price of a material is not a ranking of chemical compatibility; the right choice depends on the application.

Source: S020, S037