Composite packaging material sheet (21, 21') for the formation of a composite package (1, 1') filled with a pourable product comprising at least: - a packaging material sheet base comprising a multilayer packaging material having a designated opening; and - an opening device (3, 3') applied on the packaging material sheet base and about the designated opening and designed to seal the designated opening and being controllable in an open position so as to free at least a portion of the designated opening; wherein the packaging material sheet base comprises at least a first face and a second face opposite to the first face; wherein the second face is designed to define an inner surface of the composite package (1, 1') to be formed from the composite packaging material sheet (21, 21'); wherein the packaging material sheet base comprises a plurality of crease lines delimiting a plurality of panels; wherein the opening device (3, 3') comprises a base frame for coupling the opening device (3, 3') to the packaging material sheet base and about the designated opening; wherein the base frame comprises at least a first flange connected to the second face and having a rectilinear peripheral portion; wherein the rectilinear peripheral portion is parallel to one respective crease line defining a reference crease line; wherein the first flange is molded onto the second face; characterized in that exactly one panel comprises the designated opening; and in that the rectilinear peripheral portion is adjacent to said one respective crease line defining said reference crease line and a distance between the rectilinear peripheral portion and the reference crease line is equal or less than 2,0 mm. - a packaging material sheet base comprising a multilayer packaging material having a designated opening; and - an opening device (3, 3') applied on the packaging material sheet base and about the designated opening and designed to seal the designated opening and being controllable in an open position so as to free at least a portion of the designated opening; wherein the packaging material sheet base comprises at least a first face and a second face opposite to the first face; wherein the second face is designed to define an inner surface of the composite package (1, 1') to be formed from the composite packaging material sheet (21, 21'); wherein the packaging material sheet base comprises a plurality of crease lines delimiting a plurality of panels; wherein the opening device (3, 3') comprises a base frame for coupling the opening device (3, 3') to the packaging material sheet base and about the designated opening; wherein the base frame comprises at least a first flange connected to the second face and having a rectilinear peripheral portion; wherein the rectilinear peripheral portion is parallel to one respective crease line defining a reference crease line; wherein the first flange is molded onto the second face; characterized in that exactly one panel comprises the designated opening; and in that the rectilinear peripheral portion is adjacent to said one respective crease line defining said reference crease line and a distance between the rectilinear peripheral portion and the reference crease line is equal or less than 2,0 mm.