A butyl rubber ionomer having improved adhesion to substrates whose surfaces have polar functional groups. Examples of such substrate materials include stainless steel, glass, mylar or Teflon.RTM.. The adhesion of the butyl rubber ionomer to the substrate is at least 25% greater than the adhesion of a non-ionomeric butyl rubber to the same substrate surface and with certain substrates is more than 150% greater. The adhesion is improved with increasing levels of multiolefin content in the butyl rubber ionomer. The adhesion is greatest for butyl rubber ionomers having a high multiolefin content (at least 3.5 mol% of multiolefin monomers or at least 1.5 mol % of residual multiolefins). By taking advantage of these high adhesion levels, a composite article can be formed between the butyl rubber ionomer and the substrate.