Glass flake modified epoxy coatings were formulated as a possible barrier coating to prevent or limit the leak of radioactive gases generated by irradiated graphite. Helium gas was chosen as the test gas. The reduction of the helium gas permeability was evaluated using a helium leak detector fitted with a mass spectrometer. Both electron microscopy and microfocus x-ray tomography were used to characterize the composite morphology. Results indicate that the gas permeability of polymer coatings was significantly reduced by up to three orders of magnitude by incorporating glass flakes into the epoxy resin matrix. The application of a multilayer technique limited settling of the glass flakes which further improved the orientation of the flakes parallel to the substrate surface. The orientation of the glass flakes within the polymer matrix with respect to the substrate surface was found to play a significant role in reducing the helium gas permeability. The helium gas barrier properties of the glass flake filled epoxy resin coatings were modeled by applying tortuosity factors. (C) 2012 Elsevier B.V. All rights reserved.