Composite elements having the following layer structure: (i) from 2 to 20 mm of metal, plastic or wood, (ii) from 10 to 300 mm of polyisocyanate polyadducts, (iii) from 2 to 20 mm of metal, plastic or wood, the layer (ii) containing prefabricated polyisocyanate polyadducts (x) which are adhesively bonded by polyisocyanate polyadducts (xx) to the layers (i) and (iii), and the polyisocyanate polyadducts (x) being pieces having a volume of from 4 to 1 000 cm3.