The moisture barrier property of AlxOy, coated poly(ethylene terephthalate) (PET), poly(ethylene naphthalate) (PEN) and poly(carbonate) (PC), have been investigated. The differences in the morphology of the AlxOy, sputtered grown on these substrate were investigated using atomic force microscopy (AFM). The initial growth of the AlxOy followed closely the topology of the substrate and an amplified roughness was observed. In the fully grown AIO,, the comparative roughness followed that of the substrates. It has been found that a single layer AlxOy, improved the moisture barrier of PET by an order of magnitude, PC by two orders of magnitude while no improvement was observed for PEN. UV-ozone treatment on PC further improved the moisture barrier, while no improvement was observed for PET and PEN. The comparative effects of the substrate surface roughness and surface energy on the moisture barrier are discussed. (c) 2004 Elsevier B.V. All rights reserved.