The present invention provides a nanocomposite of an elastomer, a polymer or oligomer functionalized with a polar group, and a clay. The nanocomposite can be a mixture of a halogenated elastomer, an acid or acid anhydride modified polymer, and a clay, desirably an exfoliated clay, suitable for use as an air barrier. Also disclosed is a nanocomposite that can be a mixture of a halogenated elastomer, a polymer modified with a carboxylic acid, and an organoclay.