Abstract: Nanocomposite layered materials are prepared by co-intercalation of an onium ion surface treatment, preferably an alkoxylated onium ion and an ethylene vinyl alcohol oligomer or polymer between the layers of a nanoclay. The spacing of adjacent layers is expanded at least 3 Å, and up to 15-20 Å with the alkoxylated onium ion surface treatment. The intercalation of the ethylene vinyl alcohol polymer then increases the spacing of adjacent layers to generally about 28 Å. Improved O2 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.