Abstract: Nanocomposites are prepared by co-intercalation of a multi-charged onium ion spacing/coupling agent and a matrix polymer between the planar layers of a swellable layered material, such as a nanoclay, preferably a smectite clay. The spacing of adjacent nanoclay layers is expanded at least 3 Å, and up to 20 Å with the di-charged onium ion spacing/coupling agent. The intercalation of the matrix polymer then increases the spacing between adjacent nanoclay layers to generally about 25-30 Å. Improved O2 and CO2 gas barrier properties are observed over a broad range of humidity conditions. The resulting nanocomposite is useful for barrier layers in multi-layer packaging and for coatings.