Method for the production of foamed areal polyurethane/polyisocyanurate moldings with a thickness in a cavity of a mold, which has an inlet region, a cavity and a depressurization unit, where the method comprises the following steps: i) injection of a reactive polyurethane/polyisocyanurate mixture through at least one inlet aperture (110, 210) in the inlet region into the cavity of the mold, said cavity being under an initial pressure of 5 bar to 40 bar, preferably of 6 bar to 30 bar, particularly preferably of 7 bar to 25 bar, ii) after the injection of the reactive polyurethane/polyisocyanurate mixture, carrying out a depressurization in the cavity with a duration of 0.1 to 10 seconds, preferably 0.2 to 2 seconds, by means of at least one valve in the depressurization unit, to atmospheric pressure or to a pressure which is lower than the initial pressure and which is 1 bar to 5 bar, preferably 1 bar to 2 bar, where the reactive mixture foams along a main flow direction from the inlet region through the cavity to the depressurization unit, iii) hardening, cooling and demolding of the foamed areal polyurethane/polyisocyanurate molding, characterized in that the cavity has two long dimensions and and one dimension that is short in comparison therewith, and one of the long dimensions represents the main flow direction of the foam, the cavity has at least one wall in the plane which contains the dimensions and, or has at least one portion of a wall in the plane which contains the dimensions and, where the portion of a wall corresponds to the area which extends in the dimension across that one-tenth part of the wall that is opposite to the inlet region, and where the at least one wall or the at least one portion of a wall has at least one aperture which connects the cavity and the depressurization unit, the ratio of the sum of the areas of the at least one aperture to the area of the wall comprising said aperture or of the portion of a wall, where said portion comprises said aperture, is 1:20 to 1:100, the at least one aperture has a length in the direction of the long dimension of the cavity, and the ratio of the length and, respectively, of the sum of the lengths of the at least one aperture to the length of the cavity is greater than 1:4, preferably greater than 1:2, particularly preferably greater than 3:4. i) injection of a reactive polyurethane/polyisocyanurate mixture through at least one inlet aperture (110, 210) in the inlet region into the cavity of the mold, said cavity being under an initial pressure of 5 bar to 40 bar, preferably of 6 bar to 30 bar, particularly preferably of 7 bar to 25 bar, ii) after the injection of the reactive polyurethane/polyisocyanurate mixture, carrying out a depressurization in the cavity with a duration of 0.1 to 10 seconds, preferably 0.2 to 2 seconds, by means of at least one valve in the depressurization unit, to atmospheric pressure or to a pressure which is lower than the initial pressure and which is 1 bar to 5 bar, preferably 1 bar to 2 bar, where the reactive mixture foams along a main flow direction from the inlet region through the cavity to the depressurization unit, iii) hardening, cooling and demolding of the foamed areal polyurethane/polyisocyanurate molding, the cavity has two long dimensions and and one dimension that is short in comparison therewith, and one of the long dimensions represents the main flow direction of the foam, the cavity has at least one wall in the plane which contains the dimensions and, or has at least one portion of a wall in the plane which contains the dimensions and, where the portion of a wall corresponds to the area which extends in the dimension across that one-tenth part of the wall that is opposite to the inlet region, and where the at least one wall or the at least one portion of a wall has at least one aperture which connects the cavity and the depressurization unit, the ratio of the sum of the areas of the at least one aperture to the area of the wall comprising said aperture or of the portion of a wall, where said portion comprises said aperture, is 1:20 to 1:100, the at least one aperture has a length in the direction of the long dimension of the cavity, and the ratio of the length and, respectively, of the sum of the lengths of the at least one aperture to the length of the cavity is greater than 1:4, preferably greater than 1:2, particularly preferably greater than 3:4.