A three-layer material. The loadbearing portion consists of a PE grid to ensure the desired strength of the foil, with an aluminum metalized layer to provide its reflective capability. Prevents vapor formed during household activities from penetrating the roof structure and thermal insulation. Traps heat in the interior and prevents water condensation in the insulation layers. Thanks to its metalized aluminum reflective layer, Alpet moreover reflects a portion of the radiant heat into the interior of the building (as opposed to film without a threefold aluminum layer).