Jeff Woolf was riding down a narrow London street when an irate driver clipped his bike. The car’s fender snagged Woolf’s pedal, flinging him headlong into a curb. As ambulance workers triaged Woolf’s broken body, they marveled that his skull had remained in one piece; his helmet, they said, had saved his life. Twenty years later, Woolf saw few London bike share riders wearing helmets, so he invented a model that’s as handy as a bike itself. Called the Morpher, his creation is a full-scale helmet that folds to the size of a textbook.