Abstract: Seamless hollow-bodied objects of expanded polystyrene are made by a method in which polystyrene material in bead form is agglomerated about a solid removable core in a split mold. The mold halves are opened and the solid core is removed, leaving at least two preliminary sections in contact with the mold halves. The mold is reclosed, and an inflatable core is inserted and inflated to desired dimensions. The inflatable core is supplied with steam for its inflation and the polystyrene heating is completed. After deflation and removal of the inflatable core and opening of the mold halves, there is obtained a desired seamless hollow article having smooth surfaces inside and out.

Abstract: According to the process, the shape of the mold cavity is at least partly modified at the point where it is desired to modify the physical characteristics of the molding during production. After the synthetic material is injected into the mold and hot expanded to fill the mold, the mold cavity is expanded at the point where the physical characteristics are to be modified and the molding is allowed to expand in a complementary manner in order that the material completely fills the expanded cavity. Then there is a compression of the molding and the molding is cooled to fix its shape.