Organophilized montmorillonite-epoxy and polyurethane nanocomposites, useful for packaging applications, were prepared and their oxygen permeability was mixed, exfoliated and intercalculated, as shown by wide-angle X-ray diffraction (WAXRD) and transmission electron microscopy (TEM). The gas-barrier performance of the polyurethane composites was better than that of the epoxy composites due to more exfoliation. The average aspect ratio of the montmorillonite platelets in the nanocomposites could be estimated from the reduction in permeability by a numerical finite element approach.