is inclined at a suitable angle the molding mixture can be blown into the cavity in such a manner that when the hollow molded body has been finally compressed it will have a uniform density and also a uniform wall thickness after the mold cavity in the lower female die 1 has been filled either in the manner shown in fig5 or in the manner shown in fig6 the upper male die 2 is moved downwardly into the lower female die 1 and the molding mixture is compressed in accordance with the dimensions of the upper and lower dies as illustrated in fig7 in that figure it will be seen that the thickness of the walls of the finished molded body 5 increases in the direction towards the bottom of the body that is in the direction of the pressure a in fig8 i have illustrated another embodiment of the invention in which it is assumed that a molded element of a u shaped cross section is to be produced which is open at both ends and which has a smooth outer surface and an inclined inner surface of any desired shape in this embodiment the lower female die 1 has such a mold cavity configuration that the inner surface forms a core 102 similar to a male die and extending in the longitudinal direction of the u shaped cross section the lateral surfaces bounding the cavity forms steps 150 provided in accordance with the present invention each of these steps 150.