Allbirds unveiled what it’s calling its “most technical style to date” Thursday. Set to drop May 17, the Tree Flyer will feature a new, castor bean oil-based midsole that the eco-conscious footwear brand claims is 30 percent lighter than its long-used SweetFoam. According to Allbirds, the “SwiftFoam” midsole offers increased cushioning and energy return with…
