A poly(ethylene terephthalate) copolymer (PETG) has been metallized with various combinations of nickel (Ni), aluminum (Al), alumina (Al2O3), and silicon oxide (SiO2). The specimens that were created included 5 nm Ni/ 15 nm Al/ 30 nm Al2O3, 15 nm Al/ 30 nm Al2O3 and 5 nm Ni/ 30 nm Al2O3/30 nm SiO2 layer systems. It was found that PETG treated with silicon oxide on its surface exhibited higher transparency than was the case with the other metal coatings. Surfaces were characterized using XPS, which verified the overall thickness of the applied coating and identified chemical transformations which occur upon successive coating steps. The data show that the application of alumina can oxidize aluminum which has been previously applied. Three-point flexural testing was used to characterize mechanical properties of the coated polyester films; metallization with both Al and Al2O3 decreased both modulus and ultimate flexural strength of the films. Oxygen permeability properties of the coated films will also be presented. For the intended electronic packaging applications of these films, high oxygen barrier, optical transparency, and good flexibility are all required.