The difference in processing behavior between the synthetic rubbers and natural rubber becomes apparent when production facilities designed for processing natural rubber are used for synthetic rubbers. All the synthetic rubbers in one respect or another are harder to process than natural rubber. Under circumstances other than the present emergency, processing equipment suitable for handling the synthetic rubbers would gradually be evolved. In the present situation the synthetic rubbers must be processed with the equipment already available. In this discussion natural rubber and the general purpose synthetic rubbers, GR-S, GR-M, and GR-I, will be considered.