Compounding involves choosing the rubber, the amounts and types of vulcanising ingredients, protective agents, fillers and possibly synthetic rubbers, and mixing them together on a mill or in an internal mixer.
When developing the formulation the physical and chemical properties of the finished product must always be considered, along with processing characteristics, vulcanisation equipment available, and final cost of the product. For example, too much sulphur causes the compound to be overcured, which makes it brittle. Not enough sulphur means the compound will be undercured and porous like a sponge.
Compounds having a wide range of physical and chemical properties can be supplied to suit almost any application.