A rectangular blank has sides X and Y, where a and b are side dimensions, h is height, and r is width, or width reduced by height h, of the periphery region R of the finished packaging. The method includes: producing folding lines B in the blank parallel to side Y at these distances from the latter: B1: a1=h; B2: a2=h+a; B3: a3=2h+a; severing of two severing lines T, each starting from opposite sides X, along one of the folding lines B, or the extension thereof; selecting the distance between two end points ET of the severing lines T which are closer to an axis of symmetry S1 parallel to the side X, such that the distance corresponds to a side B″ of the finished packaging or length of a side M of a packaging insert.