Commercial poly(ethylene glycol-co-1,4 cyclohexanedimethanol terephthalate) (PETG) foils were irradiated with 16 MeV Au7+ ions and the resulting modifications in the polymer chemical structure, optical properties, and surface hydrophobicity were analyzed. Under irradiation, PETG displays a redshift in the optical absorbance edge, accompanied by a decrease in the optical gap from 3.8 eV to 2.4 eV. An overall decrease of characteristic functional groups is observed with damage cross sections varying from (1–2) × 10-13 cm2. New bands are formed linked mainly to oxidation and formation of conjugated carbon–carbon double bonds. The hydrophilicity of the irradiated surfaces increases possibly due to surface oxidation.