What were Buna S and GR-S, and how did they become known as SBR?

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truck tires being removed from their molds — rubber Truck tires being removed from their molds.

Buna S and GR-S are early names for styrene-butadiene rubber (SBR), a versatile synthetic rubber developed during the 20th century to address natural rubber shortages.1

Buna S: Developed by German chemists at IG Farben, the name "Buna" was derived from butadiene and sodium (natrium), the catalyst used in the process. Eduard Tschunkur and Walter Bock patented this specific copolymer of butadiene and styrene in 1933.1
GR-S: During World War II, the United States was cut off from its natural rubber supplies in East Asia. The U.S. government adopted the German formula, improved its production, and designated it "GR-S," which stood for Government Rubber-Styrene.1

Following the war, the material became widely known by the industry-standard abbreviation SBR, reflecting its chemical composition of styrene and butadiene. Today, it remains the most significant synthetic rubber produced globally, primarily used in automobile and truck tires.1