S.B.R. is a copolymer of styrene and butadiene, also known as Buna-S and G.R.S. (government rubber styrene), and was first produced under government control. It was the elastomer substitute for natural rubber during World War II. Its compounded properties are similar to those of natural rubber.
S.B.R.’s main use today is in the manufacture of automobile tires and seals for non-mineral oil-based brake fluid.