The lower part of a material to be molded forms a lower, seal with a die. A punch applying a molding force to the material forms an upper seal with the perimeter of the die. The space between the upper and lower, seals forms a pressure chamber that is filled with a fluid. As the punch descends into the die, the fluid is pressurized. The lower seal is a complete seal to prevent leakage of fluid into the die. The upper seal is given a clearance with the die that permits controlled leakage of fluid therepast at a rate that limits the maximum pressure in the pressure chamber while permitting the development of an adequate pressure on the material being molded.