The present relates to an apparatus for molding plastic parts which includes a cavity insert and a core insert wherein each insert has an open area on the shell or back side thereof. A device for circulating fluid through each chamber cools the inserts. In one preferred embodiment, the cavity and core inserts are made using a mold having a ceramic formulation including generally uniform size aggregate materials and carbon fibers. In certain embodiments, the apparatus further includes pressure bearing devices for absorbing molding pressure during operation of the molding apparatus.