In conventional injection molding when the molten polymer comes into contact with the relatively cool surface of the steel mold tool an instantaneous skin layer of frozen or highly viscous material is formed.

Although this is normal it has a number of consequences that are less than ideal both for the molded part and the injection molding process.

Injecting plastic into a tool whose surface is pre-heated to a temperature above the glass transition temperature (Tg) of an amorphous material or near to the melting point (Tm) of a semi-crystalline material confers numerous benefits: