The REN model may be painted and sent to the designer for study.  The REN model can also be joined with the lasted upper to get the idea of what the final completed shoe will look like. After the REN is approved, the design is sent to the metal shop. Depending on design, the metal may be cast, burned by high voltage electric discharge, or CNC cut by a computer controlled milling machine.  The molds are made from steel and aluminum. The flat rubber mold will be made from steel and cut by a CNC machine.  A midsole mold with high sidewalls and undercuts will be made from cast aluminum.  If the mold is made by casting process a REN must be made of each size, left and right. CNC cut molds don’t require every size to be cut. While most of the footwear mold is created by machine, hand work is still required to make sure everything fits correctly.  Outsole and midsole parts must fit together tightly for good bonding. After a test pressing the outsole molds are returned to the shop for some rework.  This mold shop will also repair an outsole mold that has been damaged or worn out during production.  While the mold factory may be a loud and dirty place to visit, if you want to see how Shoe Outsole Tooling is made it’s worth a visit!  You will see many types of molding equipment for shoe soles.