Wütop DB 20 from Würth is an interior roof film, used in construction, that provides an airtight, vapour-permeable (diffusive), water barrier layer. It is a three layer construction made of up high density polyethylene (HDPE) printed film top layer, reinforcing mesh, and polypropylene (PP) fleece backing layer, welded together. It prevents saturation of the thermal insulation with moisture on the room side, helping to maintain the most efficient insulation values.