a method of molding a plastic part comprising supporting first and second mold sections so as to define a mold cavity , placing a flexible sheet over the second mold section , and forming a vacuum chamber utilizing the flexible sheet with at least the second mold section being in the vacuum chamber . air passages are provided between the flexible sheet and the second mold section . the air pressure within the vacuum chamber is reduced to less than ambient to create differential pressure across the flexible sheet to hold the second mold section in position . plastic material is pumped into the mold cavity . after the plastic sets , the second mold section is removed .