Chlorobutyl (CIIR) and Isobutylene Isoprene (IIR) compounds provide superior gas permeation and excellent weather resistance. They are also useful for their energy absorption properties. Food grades are available.
Butyl rubbers do not provide good petroleum oil or fuel resistance and are not especially good at compression set resistance.
PAI offers Butyl compounds in a hardness range of 30 to 70 durometer. Black is the standard color, but some white compounds are available.