Water vapor permeability of permeation barrier films and thin film encapsulation coatings is determined both by intrinsic factors: material and technology selection and extrinsic factors: e.g. particle contamination or process defects. This paper discusses optimization strategies to achieve low permeability gas barrier films that are robust in roll-to-roll processing and integration to devices. Water vapor transmission rates of < 5·10^-4 g/(m²d) at 38°C / 90 % r.h. are demonstrated reproducibly in a full roll-to-roll process chain using a sputtered barrier layer and a protective top-coat.