The present invention is a blend of an halogenated elastomer and a clay, desirably an exfoliated clay, to form a nanocomposite suitable for an air barrier. In one embodiment, the halogenated elastomer is a polymer comprising C.sub.4 to C.sub.7 isoolefin derived units, a para-methylstyrene derived units, and para-(halomethylstyrene) derived units. In another embodiment, the halogenated elastomer is a butyl-type rubber. The clay may or may not have an additional exfoliating treatment present prior to blending with the interpolymer. The interpolymer/clay mixture forms a distinct phase in the nanocomposite blend of the invention. The blend of the invention has improved air barrier properties and is suitable as an innerliner or innertube.