Polyamide 6 (PA 6) melts and dissolves in super-heated water when T > 160 degrees C. Commercial PA 6 films were treated in super-heated water at 140 degrees C < T < 160 degrees C, i.e. below melting. Morphology, thermal behavior, mechanical properties, oxygen permeability and transparency of the film before and after hydrothermal treatment are investigated. After hydrothermal treatment, the melting temperature, crystallinity, elongation at break and toughness increase, whereas the strength decreases. The transparency and oxygen permeability decrease slightly. More interestingly, the hydrothermal treatment generates on the film surface a nano-structured layer 100 nm thick, which greatly improves adhesion and printing performance. (C) 2018 Elsevier B.V. All rights reserved.