Commercial production is by copolymerization of isobutylene with isoprene.
Halogenated butyl rubber, which accounts for over half of global consumption, is made by reacting butyl rubber in a hexane solution with bromine or chlorine. Bayer and Exxon account for by far the largest share of world production capacity for butyl and halobutyl rubber. In addition to its Sarnia plant, Bayer has 95,000 tons of capacity at Zwijndrecht in Belgium. Japan Butyl Company, a 50-50 joint venture of Exxon with Japan Synthetic Rubber Company, has capacity for 80,000 metric tons of butyl rubber at its Kawasaki plant in Japan and 25,000 tons of halobutyl rubber at Kashima. Exxon has 50,000 tons of capacity idle at its Baytown site.