The surfaces of untreated and helium plasma-based ion implantation (He PBII) treated poly(ethylene terephthalate) (PET) samples were characterised by reflectance colorimetry, contact angle studies and measurements of surface electrical resistance. The results were related to the structural and compositional data obtained by the authors earlier on parallel samples by XPS and Raman spectroscopy. Inverse correlations between lightness and I(D)/I(G) ratio and between chroma and I(D)/I(G) ratio were obtained, suggesting that the PBII-treated PET samples darken and their colourfulness decreases with the increase of the portion of aromatic sp(2) carbon rings in the chemical structure of the modified layer. Direct correlation between water contact angle and the I(D)/I(G) ratio and inverse correlations between surface energy and I(D)/I(G) ratio and between dispersive component of surface energy and I(D)/I(G) ratio were found, reflecting that surface wettability, surface energy and its dispersive component decrease with the formation of surface structure, characterised again by enhanced portion of aromatic sp(2) carbon rings. The surface electrical resistance decreased with the increase of the surface C-content determined by XPS and also with the increase of the surface concentration of conjugated double bonds, reflected by the increase of the pi ->pi* shake-up satellite of the C 1s peak. (C) 2011 Elsevier B.V. All rights reserved.