Separating membrane of plastic material, made up of a bossed and waterproof sheet which is coupled with a permeable base layer. The bosses are of the cylindrical type with a double diameter and have such a shape and arrangement as to feature improved adhesion on both faces. The gripping of the adhesive is increased in order to obtain greater tear strength, on the upper face, and at the same time increases the area of contact with the base layer for a greater resistance to delamination on the lower face. In particular, inside each chamber there is an internal crown, which divides it like a necking into two superimposed compartments having the same diameter, wherein the first compartment has a depth amounting to at least ⅓ of the total. A production process for obtaining the membrane is also disclosed.