The mass transport properties of composite systems resulting from the dispersion of impermeable platelets in a permeable matrix have been discussed on the basis of the results of a numerical analysis of the problem. In particular, 2-D ordered structures with platelets oriented normally to the average mass flux in the system have been analyzed by using a CFD algorithm, based on a finite volumes method, and the increase of barrier effect is discussed as function of filler loading, platelet shape and dimensions, and arrangement of platelet layers. The numerical solutions obtained were compared with the models most commonly used for correlations of apparent permeability and a new formulation capable to predict the gas transport properties in this simplified nanocomposite geometries has been proposed, based on revision of earlier theories. This relationship correctly describes the enhancement in barrier effect for the systems analyzed for a wide range of filler loading and platelet dimensions and can be reliably used to obtain relevant information on gas permeability in real nanocomposite systems. (C) 2008 Elsevier B.V. All rights reserved.