FIN is a concept for a running shoe sole that was developed in collaboration with ON running. The sole adapts to different running styles. Inspired by the underwater world and the movement of manta rays, the structure of the cavities is designed to allow the sole to flex. By utilizing the fin ray effect, the sole adapts to the runner's foot and provides both cushioning and rebound. The shape of the sole allows it to be produced by extrusion. The use of TPU monomaterial makes it cost-effective, requires little manual labor and is easy to recycle.