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More than 2 billion car tires are manufactured every year. They’re made from both synthetic, or artificial, rubber and natural rubber from rubber trees. Rubber trees grow only in tropical areas, mainly Southeast Asia, and are prone to disease. So tire-maker Bridgestone has been investigating another source of natural rubber: guayule (why-oo-lee). This hardy shrub grows in dry climates.

“Rubber is a polymer, a material made up of a chain of molecules linked together,” says Catherine Brewer, a chemical engineer at New Mexico State University. Rubber’s chemical structure makes it stretchy and tough—perfect for car tires. Bridgestone believes sourcing rubber from guayule is more sustainable, or environmentally friendly. This past spring, the company debuted tires containing guayule rubber at an IndyCar race in Tennessee.