The molds are key pieces in the process must have the following basic requirements:
- The material from which they are made must have a good thermal conductivity so that the heat is transferred or removed from the plastic as quickly as possible
- Must have sufficient mechanical strength to remain unbalanced during the heating and cooling cycles to which they must be subjected
- The two parts of the mold must have a closing system that allows to close it tightly and open it with simplicity
- They must be able to be mounted on the arm or plate so that the circulation of the air around them is not impeded
- Must have a vent that has the function of maintaining the pressure inside the mold equal to atmospheric. This is very important if one takes into account the large volume of air that is housed inside the molds and the large temperature variation that occurs throughout the cycle.