IIR (Butyl) - CIIR (Chlorobutyl) - BIIR (Bromobutyl) rubber Butyl rubbers are isobutylene copolymers, having a small quantity of isoprene. Its main characteristics are: high water-proof high heat resistance high resistance to ozone high resistance to ultra-violet rays. When butyl compounds (or halo-butyl compounds) are correctly formulated and processed, the vulcanizates show an excellent resistance against basic and chemical products and show a very low permeability to gases and liquids. Butyl (or halo-butyl) compounds are suitable to work at the maximum temperature of 120°C.