Titanium films, 1 μm thick were electron‐beam evaporated onto polyethylene (PE) that had been pretreatedinsituby 2 keV Ar+bombardment. A measure of the film adhesion was obtained by measuring the pull strength required to remove the Ti films. A strong dependence of the adhesion on the ion dose was found. The pull strength had a maximum of approximately 20 MPa after a dose of 6×1014ions/cm2but decreased for higher ion doses. Without any ion bombardment prior to deposition, the adhesion was very poor with a pull strength of approximately 2 MPa. XPS analysis was used to examine the effect of the ion bombardment on the chemistry of the PE substrate and the Ti/PE interface. Untreated PE samples were contaminated with surface impurities and probably also with low molecular weight hydrocarbons. As the adhesion is maximized, most of the impurities are removed by the ion bombardment. The strong adhesion is suggested to be due to formation of a carbidelike Ti–C interfacial layer, detected by XPS.