Rather than use melt­ed plas­tic to fill the cav­i­ties of the mold, the com­pres­sion mold­ing method involves pour­ing or plac­ing ther­moset mate­ri­als into a heat­ed mold cav­i­ty. The mold is then com­pressed under heavy pres­sure, forc­ing the mate­r­i­al to spread through­out the mold. To ensure prop­er cur­ing, com­pres­sion molds must be kept at a sta­ble pres­sure and tem­per­a­ture.

Com­pres­sion mold­ing can be slight­ly less con­sis­tent than injec­tion mold­ing and is bet­ter suit­ed for less com­plex com­po­nents. While both types of mold­ing can yield high-vol­ume out­put, com­pres­sion mold­ing is more afford­able for build­ing sim­ple com­po­nents that are strong and durable. Anoth­er advan­tage of com­pres­sion mold­ing is the abil­i­ty to pro­duce extra-large parts at low­er cost.