The effect of plasma treatment on surface characteristics of polyethylene terephthalate films was investigated using helium and oxygenated-helium atmospheric plasmas. Sample exposure to plasma was conducted in a closed ventilation test cell inside the main plasma chamber with variable exposure times. The percent weigh loss of the samples showed an initial increase followed by decrease with extended exposure time, indicating a combined mechanism of etching and redeposition. The wettability as measured by the contact angle showed a sharp initial increase followed by a steady-state trend with increased exposure time, suggesting a change in surface functionality. Atomic force microscopy analysis revealed increase in surface roughness, as well as evidence of redeposition of etched volatiles. Functionality changes were measured using X-ray pholoelectron spectroscopy and these changes were correlated to the new plasma-induced properties. (C) 2004 The Electrochemical Society.