When materials such as, Silicone, Expoxy Resins, Araldite and Polysulphide Rubbers are mixed with the required additives, air bubbles can become trapped within the mixture. If not removed before the material cures the air bubbles can cause defects such as nodules, cavities and hollows in the finished cast.

With electronic encapsulation these air bubbles can cause breakdowns and if present within intricate castings additional work will be required to correct the defects caused by the air bubbles.

The majority of these materials will expand during the degassing process. It is essential that a container of sufficient volume is used. It is not uncommon for materials to expand two to six times their initial volume while degassing.

As the bubbles burst at the surface the expansion decreases. This process can take several minutes depending on the viscosity of the material, the speed of the vacuum pump and the volume of the vacuum chamber.