For Bridgestone, one of the most prominent renewable materials is guayule. Over more than a decade the tire maker has invested more than $100 million in the cultivation, study and scale-up of the alternative natural rubber. And that investment has proven itself, Shaffer said, pointing to the ways in which Bridgestone has incorporated the guayule in its products—specifically a 75-percent sustainable materials demonstration tire and the sidewall of the Firestone Firehawk racing tires.