This study investigates the two possible mechanisms of ink refusal by the non-image area of waterless offset printing, i.e., the formation of a weak fluid boundary layer on the non-image area and the softening of the non-image area after contacting with ink. FT-IR-ATR, Micro-Indentation, AFM and a Deltack Printability Tester were used to analyze the plate surface before and after the plate-ink contact. Our results show that the dominant ink refusal mechanism is the softening of the non-image area caused by the possible diffusion of low molecular weight hydrocarbon components in ink diluents into the polymeric layer of the non-image area. The formation of a weak fluid boundary layer is also likely to contribute to ink refusal and may play a synergistic role. (C) Koninklijke Brill NV, Leiden, 2009