Prefabricated modified composite polymer-bitumen waterproofing membrane, manufactured with patented technology, composed of distilled bitumen and differentiated waterproofing masses. The upper face compound is composed of distilled bitumen, polyolefins and elasto-plastomers (APP) while the lower face compound is composed of distilled bitumen and elastomeric polymers (SBS). A special compound, specifically designed, is used to promote the compatibility between the APP and SBS. The upper face waterproofing mass has excellent ageing properties, walkability, cold flexibility heat and UV resistance, while the lower face waterproofing mass has excellent cold flexibility and adhesion to the substrates. The P and PA versions are reinforced with a triple reinforced fabric composed of a fiberglass mat sandwiched in between two layers of woven non woven single strand composite polyester, having excellent mechanical characteritics and exceptional dimensional stability. The P version, on the upper face, has a woven non woven polypropylene mat finish. The PA version is self-protected with mineral slates which reduce heat absorption and improve the durability of the membrane. PLURA HP TRIARMATO has a 10 cm side selvedge and a 15 cm head selvedge which promotes the adhesion between the sheets.