Polymer/clay nanocomposite (PCN) membranes are useful as barrier materials to reduce the permeability of gases and vapors through polymer materials. Extensive studies have focused on theoretical prediction of the effective diffusion coefficients based on the clay fraction and distribution within the polymer matrix. However, existing models are based on highly idealized geometries of the PCN membranes, and are not in agreement with experimental data as a consequence. A simple and novel numerical method based on a two-dimensional representation of the barrier membrane is developed to predict gas permeability in PCN. Employing Transmission Electron Microscopy (TEM), the nano-structure of PCN is captured and transformed into mathematical morphology data. Based on the image matrix, the barrier property of PCN was numerically modelled and generally agrees well with experimental measurements from the literature for volatile organic compounds. Because the geometry of barrier polymers can be easily captured by TEM, the proposed method should be applicable to different PCN membranes to quickly estimate the barrier properties for gases and vapors. (C) 2016 Elsevier B.V. All rights reserved.