In a process for the production of composite elements which have the following layer structure: (i) from 2 to 20 mm of metal, plastic or wood, (ii) from 10 to 300 mm of plastic and (iii) from 2 to 20 mm of metal, plastic or wood, the starting materials for the production of (ii) are introduced in the liquid state in at least two steps into the space between (i) and (iii), the space to be filled in the last filling process having a volume of from 0.1 to 1.5 m.sup.3 and the height of the space to be filled being less than 25 mm.