The folding doors allow to reduce the sash overall dimensions when the door opened. In fact, the door opens like a book, bending. The Piego opening system foresees that the door is divided in half in a symmetrical manner. The series of hinges are retractable, for a very pleasing aesthetic effect. When the door open does not invade the room with the leaf size, but takes some of the free space of passage; situation to be taken into account when choosing the models of doors for our home.