I.Based on molding plastic material, molds can be classified into:

1. Thermoplastic injection die；
2. Thermosetting plastic injection die；
3. Elastomer plastic injection die (such as rubber and silica gel molds)；
4. Structural foam plastic injection mould；
Of which the injection molds are classified into two-plate molds and three-plate molds

II.The most frequently adopted molds are thermoplastic injection molds

1. Thermoplastic characteristics:
This kind of plastic will soften during heating, and will turn into molten state when the temperature reach a certain value , and the flexible viscous liquid will be formed into required products with the help of moulds and pressure, and the formed product will remain its shape after cooling. When the product is heated again, it will soften, melt and be formed into specified shape once again. There is only physical change without any chemical change during heating and cooling processes. Normally most ordinary plastic materials are of this type. And this is also the feature of plastic products to be used as a criteria to decide whether or not conduct die sinking.
2. Thermosetting plastic characteristics:
This kind of plastic will soften during heating, and cure to specified shape with stiffness after cooling. It will not soften again during reheating and will diffract when the temperature reach a certain value. This is because chemical change happens during molding process, and thread molecules change into body molecules, resin changes into non-softening non-dissolvable, unchangeable shape. It has no plasticity any more and is hard and brittle. Typical thermosetting plastic includes PF, UF, MF, EP, UP etc.
3. Classification according to plastic applications
A. Common use plastics
This kind of plastic is widely adopted in various applications. It has big output and low price which accounts for three quarters of the overall output of plastics. Most of it is used to produce daily use goods bearing low stress such as television casing, moulds for household electrical appliances etc.. Common used plastic includes ABS，PP, PE, PVC, PS etc.
B. Engineering plastics:
Common use plastic is cheap, however its mechanical property, temperature-withstanding and corrosion-prevention performances can not meet specific requirements of structural materials in some engineering and equipment. Thus engineering plastics comes into being. It has high mechanical strength, high stiffness and it can substitute for some steel or non-ferrous materials, can be used to manufacture mechanical parts with complicated structure or engineering components under stress. Most of these new parts exhibit better performance than parts made of original materials. Common used engineering plastics include POM, PC, PA, PTFE etc.
C. Special plastics
This kind of plastic has some distinct functions which can be used in special applications, such as magnetic conductive plastic, pharmacal-use plastic, pearl luster plastic, photo-plastic etc.