Polyethylene film was modified by addn. of microcelulose (3% or 8%), Zn (5% or 8%), 5% Ag nanoparticles or a bio-stimulant based on Ag nano particles, and tested for insulating properties important for plant silages prodn. based on grasses and legumes. Populations of lactic acid bacteria, aerobic bacteria, mold and yeast were detd. for the polyethylene films, after 5, 8 and 18 mo. long fermentation. The film with 5% addn. of Zn was the most advantageous for the prodn. of the silage.