In compression molding, a preform is placed on one half of a heated mold. When the mold is closed and put under pressure (in a press), the rubber is forced into all parts of the mould cavity; and excess rubber flows into a flash groove around the mould cavity.

Silicone rubber is compression-molded to form gaskets, seals, O-rings, flat sheets, fabric reinforced laminates, and many other types of industrial rubber goods, of almost any size desired.

Compression molding was specifically developed for replacement of metal components with composite parts. The molding process can be carried out with either thermosets or thermoplastics. However, most applications today use thermoset polymers. In fact, compression molding is the most common method of processing thermosets.