Butyl is a synthetic rubber, a copolymer of isobutylene and isoprene. Butyl exhibits an extremely low gas permeability rating, making Butyl orings ideal seals in the military industry sealing gas mask and protective clothing. Butyl orings are also found in many other industries due to its diverse chemical resistance properties. Butyl o-rings are also referred to as isobutylene-isoprene orings or IIR o-rings. We can offer a complete selection of both the standard AS568 o-ring and metric o-ring sizes. We can also develop custom Butyl o-rings to meet customer applications or specifications.