Prefabricated modified polymer bitumen membrane composed of polyolefin thermoplastic stereospecific polymers with high molecular weight and special distilled bitumens, with excellent characteristics of resistance to ageing and phase inversion (type APP). These built in elements, integrating themselves, enhance the excellent qualities of flexibility, lightness, adhesion, resistance to ageing and to UV rays of the LARIX P+V membrane. The dual reinforcement with a woven non woven single strand polyester and rot proof fiber glass mat, confer to the product high mechanical characteristics and excellent dimensional stability. The fiber glass is positioned in proximity of the upper face of the membrane guaranteeing a longer durability. The LARIX P+V membrane is finished on the upper face with a special talc. On the application face, the membrane is finished with a woven non woven polypropylene mat, suitable for both application with adhesive cold bond glues, as well as on LARIX THERMOADHESIVE.