The raw EPS beads (EPS= expandable polystyrene) are delivered at a density of about 38 #/cubic foot in a wide range of initial sizes (10 to 80 mils diameter)  

• The smallest beads give the best fill into the tool and surface finish, but they are more difficult to control for uniform density.
• As a rule of thumb, the thinnest wall section in the casting should allow at least a three (3) bead fills wide after curing.  This generally limits wall sections to sizes greater than 3 mm (0.120 inches) for aluminum. 

• Preexpansion by heat and conditioning of the beads to control and stabilize the bead size and density for molding
• Preheating the metal tool to the desired cure temperature
• Injection of the beads into the tool
• Heat and cooling the tool to expand the beads and fuse the pattern.