Abstract: A composite slab made of plastic, especially polypropylene, for construction purposes and packing purposes for example is described, said slab according to a preferred embodiment comprising a plurality of layers, each of which consists of a composite that is extruded in a plurality of layers and of which two plane layers and the others are profiled, namely layers that have a corrugated profile with peak lines that are located in a plane, with these layers being welded together along the peak lines on one side of the profiled layer and/or at the intersections of the peak lines of adjacent profiled layers. Layers consisting of a plane slab can be provided between the profiled layers. The composite extruded in several layers comprises two outer layers and a middle layer made of polymers from the same material group, whose middle layer consists of a highly crystalline polymer with incorporated stretch-resistant fibers, whose melting point is at least 15.degree. C.