Alternating (A B A) polymer films with individual layer thicknesses in the 3-25 mu m range were produced using a robust layer multiplying coextrusion process. Such a film with layers of a poly(propylene-graft-maleic anhydride) (PPgMA) alternating with layers of PPgMA containing a phosphate glass (Pglass) upon biaxial orientation exhibited percolation of high barrier filler platelets resulting in reduction in gas permeation by two to 3 orders of magnitude. This unprecedented reduction in oxygen permeability was attributed to the high volume fraction of highly aligned Pglass platelets in the polymer matrix resembling a brick wall microstructure. Biaxially oriented films with 20 vol % Pglass content exhibited a microstructure resembling alternating organic and inorganic layers, a close replica of natural biocomposites. Structural models for permeability indicated that enhanced barrier resulted from increased tortuosity of the diffusion pathway provided by the aligned high aspect ratio platelets. Aspect ratios ranging from 40 to 175 were calculated by fitting the experimental data to diffusion models. Mechanical tests revealed that the presence of Pglass platelets increased the modulus of the multilayer composites by as much as 2x, without any considerable loss in ductility. The improvement in mechanical properties was ascribed to the high aspect ratio of the oriented Pglass platelets. Biaxially oriented films conditioned at high relative humidity (97% RH) maintained their high oxygen barrier properties. With an optical transparency between 60 and 85%, and good flexibility, these films stood out as good candidates for a variety of packaging applications.