Factice is vulcanized unsaturated vegetable or animal oil, used as a processing aid and property modifier in rubber.
Longer chain fatty-acid containing oils such as rapeseed or meadowfoam produce a harder, more desirable factice.
Soybean oil produces lower quality factice, though it can be mixed with longer-chain oils to yield factice nearly as good as that made from long chain oils alone.
[1] Oil-resistant factice is made with castor oil.
[2] Cross-linking the fatty-acid chains with sulfur (brown factice) or S2Cl2 (white factice) yields a rubbery material that improves the processing characteristics and ozone resistance of rubber.