Lightweight filler for waterproofing bitumen membranes

A waterproofing membrane comprising a reinforcing material that includes a blend formulation, wherein the reinforcing material forms a reinforcement layer positioned between two layers comprising the blend formulation, and a torching foil as the bottom most layer in the waterproofing membrane, wherein the blend formulation is solid at room temperature and comprising:

• 50-90% w/w bitumen or 50-90% w/w mix of bitumen and plasticizer;
• 2-25% w/w elastomeric block co-polymer;
• and
• 5-45% w/w glass spheres having a particle size between 0.25-0.50 mm and a particle density between 0.5-0.8 g/cm3, wherein interior of each glass sphere is filled with air pockets making it neither hollow nor solid but porous.