A characterisation of a low pressure SF6 discharge was undertaken, by means of plasma diagnostics, including radiofrequency electrical probes, Langmuir probes and optical emission spectroscopy. Chemical kinetics modeling of the discharge was performed too. This was aimed to the understanding of a reported transition in the plasma induced surface modification on poly(ethylene terephthalate) (PET) fibres by SF6 plasma treatment which can be characterized as a striking wettability modification reverse displayed by plasma treated fibres as the SF6 pressure in the discharge exceeds a threshold value. Here we have investigated the modification also on different polymeric surface such as that of a PET film and of cellulose (paper). We point out that the observed transition could be understood as a switch between an increased surface hydrophilicity, induced by plasma treatment at low pressure, which produces also surface etching and activation, and an increased surface hydrophobicity, imparted by plasma treatment at higher pressures, due to extended surface fluorination.