Abstract: A double belt system for producing a prefabricated construction element includes a conveyor system for discontinuously or continuously conveying a first panel, a conveyor system for conveying a first lateral border profile operating as a framework, an application device for applying a foaming plastic material on the first panel and between the first lateral border profile operating as framework and a lateral edge border disposed opposite the first lateral border profile. The double belt system has a top belt and a bottom belt, and at least one protrusion disposed in the belt of the double belt system and facing the first panel and extending circumferentially in the rotation direction of the belt. A recess which is set back in relation to a flat surface is formed in the foamed plastic material with the at least one protrusion.