Barrier membranes with carefully patterned metal flakes have been prepared by means of photo lithography. The shape, aspect ratio and volume ratio of the metal flake are varied. The flakes are typically 100 micron square and 1 micron thick, present at volume fractions of 0.10. Gas permeation experiments carried out using these composite barriers show permeability reductions which are over two orders of magnitude. Complementally mechanical measurements show how these permeability reductions are gained at a cost of poorer flexibility and toughness. These permeability and mechanical measurements are compared with available theories to discover how films with low permeability and high flexibility can be made.