The objective of this study was to manufacture and investigate the properties of barrier films made from microfibril-reinforced polymer composites (MFCs) based on blends of linear low density polyethylene (PE) and poly(ethylene terephthalate) (PET). Blends containing 30 wt% of PET were prepared and extruded into strands. These were then subjected to cold drawing and compression moulded into thin films. The permeability of the films to oxygen gas was measured using a permeation test chamber and the effect of the draw ratio on the size of the reinforcing fibrils was also observed. Scanning electron microscope (SEM) revealed substantial differences in the structures of neat and MFC films. A model developed for predicting the permeability of filled polymer composite films was modified and compared to the test results. The draw ratios of the MFCs did not appear to have a significant effect on oxygen permeation, despite altering the dimensions of the reinforcing fibrils. The MFC films were found to be half as permeable as the neat polymer films.