A device for the application of foaming reaction mixtures to a substrate which makes it possible to apply that foaming reaction mixture uniformly, a process for the production of foaming reaction mixtures using this device, apparatus for producing composites which include the device of the present invention and composites produced using such apparatus are disclosed. Use of the device of the present invention to produce foams makes it possible to produce foams having improved surface quality at higher production rates than were previously possible. The device of the present invention is particularly useful for the production of sandwich composite elements.