Process oils were, and still are today, the go-to choice for plasticizers in a rubber formulation. Process oil acts as an extender in the formulation, making the mixing process faster and more efficient. It’s important to choose good polymer compatibility, as the process oil can influence the rubber’s softness, stability, and ultimately performance the finished product. The three main types of process oil utilized by the rubber industry are aromatic, naphthenic, and paraffinic.