The invention relates to a method for the production of polyurethane block foam, wherein a polyurethane reactive mixture containing carbon dioxide is suddenly relieved from a pressure above the pressure breaking the equilibrium of the carbon dioxide to a normal pressure, wherein the liquid polyurethane reactive mixture is foamed by releasing dissolved carbon dioxide. The foamed mixture is placed on a substrate and then hardened into block foam, wherein the carbon dioxide or at least one of the components polyol and isocyanate is initially dissolved in the reactive mixture at a pressure that is substantially above the pressure breaking the equilibrium, the pressure is subsequently lowered to a pressure close to the pressure breaking the equilibrium, wherein the pressure falls below the pressure breaking the equilibrium by releasing small amounts of carbon dioxide and forming a microdispersion of bubbles, the components are optionally mixed and a sudden pressure drop to normal pressure occurs before the carbon dioxide released is completely dissolved.