Pre-fabricated waterproofing membrane for specific use as a total barrier to the passage of vapour. The waterproofing mass is made of distilled bitumen and elastoplastic polymers (APP), reinforced with a rot proof fibre glass reinforcement and aluminium film which allows to obtain a barrier to the transmission of vapour. Due to the characteristics, the membranes of the POLIGUAINA AL range are used with success in the waterproofing of both civil and industrial works where required, with the use of thermal insulation, as an absolute barrier to the transmission of water vapour. In the stratification of the roof, the POLIGUAINA AL must be positioned under the insulation, in order to preserve it from phenomena’s of water vapour condensation, which surely occurs, with the excursion changes of the thermal conditions of the roof.