The present invention provides a nanocomposite of an isobutylene-based elastomer and a phosphate nanofiller. Also disclosed is a nanocomposite embodiment wherein the elastomer is BIMSM and high aspect ratio, partially intercalated, partially exfoliated alpha-zirconium phosphate treated with amine or amide. A dispersion aid can include a low molecular weight polymer or oligomer, optionally functionalized with a polar group. The nanocomposite is suitable for use as an air barrier.