Polymer-clay nanocomposites have been prepared by solution intercalation of poly(vinyl alcohol) (PVOH) into Na + Montmorillonite (Na + Cloisite ( R)). XRD has been used to determine the dispersion of the individual clay platelets in the PVOH matrix. ATR-FTIR has been used to perform in situ diffusion experiments of water and acetone into nanocomposite films. The data has been compared to that obtained from the pure polymers to evaluate the barrier properties of the nanocomposites. The dominant process during water uptake was polymer solvation so the clay loading exerted little influence on the uptake rate. In contrast, the rate of diffusion of acetone was significantly reduced as the clay loading in the nanocomposite increased.