Three different theories dealing with mass transport through polymer-clay nanocomposites are discussed. The first one is a Langmuir type model; the second one is a Drozdov type model and the third one is a mesoscopic model. The Langmuir and Drozdov type models address adsorption of the solvent on the clay particles, while the mesoscopic model relates the viscoelastic properties of the polymer chains to the diffusion process. Experimental results of water moisture through vinyl ester nanocomposites made with two different clay particles are modeled and discussed. (c) 2007 American Institute of Chemical Engineers.