Geomembranes are thin, flexible sheets with very low permeability. They are manufactured in a controlled factory environment starting from a mix of polymeric resins and additives, which is extruded to form the sheets. Performance properties of the final product depends on the characteristics of the single components, on the specific material design, and on the manufacturing method. Critical properties of a geomembrane for lining hydraulic structures are: imperviousness, which must be maintained over the whole service life of the structure; strength and elongation capability, which must enable the geomembrane to withstand deformations of the underlying support; resistance against ageing, so to enable an acceptable service life. Leakage through a hydraulic structure can affect its efficiency if not become a threaten for its safety. Geomembranes with proper performance properties can be essential in ensuring efficiency, reliability and safety of hydraulic structures. This paper describes a fewamong the \u3e250 projects that have been performed by the affiliation of the authors
