PET preform mold may be defined as a form for shaping a plastic material "PET" into a finished product-here is PET preform. PET preform molds are made of plain carbon steel or of alloy steels, and are hardened to provide compressive strength and hard surfaces to take and maintain a high polish under severe wearing conditions. PET preform molding materials require heat and usually pressure to achieve the plasticity necessary for them to flow into the shape of the mould cavity. Pressure is required to force the material into the cavity and to hold it to shape until it is set, and to give the casting or finished product the required strength. A PET preform mold must be polished to give the casting a good finish，and to allow it to be ejected easily.

To design plastics PET preform molds, a plastics engineer should have an intimate knowledge of a proper design procedure which is based upon a knowledge of the characteristics of materials; of the technique of PET preform mold building; of the economics of each production schedule; of the tooling cost both to purchaser and to the PET preform mould manufacturers; of PET preform moulding equipment operation; of the special mould steels and alloys; and of the moulding and finishing facilities of his own plant.

The design of plastic PET preform molds includes, besides the design of the mould proper, the provision for mounting the mould in a press; the provision of means to eject the finished PET preform molded casting; and a provision for temperature control. There are also finishing tools to be designed, such as drilling jigs, buffing attachments, holding fixtures, cooling fixtures, gages, and other devices for obtaining accurate and economical production.