Abstract: An apparatus for manufacturing continuous webs of polymer foam obtained from a mixture of liquid reagents, wherein the volume of a container is determined to form a zone of retention of the mixture of reagents in liquid phase and wherein the level of this mixture is maintained at a level slightly higher than the plane upon which the mixture in the liquid state flows, so that the primary phase of expansion of the mixture and its further expansion are produced outside the container on a moving surface of the conveyor, which surface is maintained in a substantially horizontal plane. The invention is particularly applicable to the production of webs of supple foam or of panels of rigid foam.