Flexible monolayer films with modulated diffusional and optical properties were achieved from blends of a LDPE/LLDPE matrix and an ethylene/norbornene copolymer (COC). A significant decrease of O-2 and CO2 permeability was observed for cast films with COC content from 5 to 20 wt %. SEM analysis showed that, despite the incompatibility of the blend components, good dispersion and distribution of the COC domains in the PE matrix were achieved; as a consequence, for COC content ranging from 5 to 10 wt % the film transparency results practically unchanged. The UV light transmission decreased on increasing the percentage of COC, which constitutes also a protection against UV radiations. A noticeable improvement was observed in the mechanical properties: adding only 5 wt % of COC, the elastic modulus becomes five times higher than that of the PE matrix. The rheological behavior of the blends keeps practically unchanged with respect to the matrix, allowing to use the typical LDPE processing conditions. Sustainable inexpensive flexible films answering the packaging requirements of specific categories of food were achieved. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121:3020-3027, 2011