The Endorphin Pro launched in February of 2020, but the road to get there was long and uphill. We tried multiple upper designs. We opened eight unique sets of casted metal bottom unit molds. We tested a number of carbon fiber plate layups (the order and direction of carbon weave construction.) We moved the shoe from a 4mm offset to an 8mm offset … for those wondering why: These new materials are incredibly soft and elastic. When fully loaded in strike, the shoe compresses far more than foams of the past. We refer to this loaded thickness the “effective stack height”. A 36mm tall shoe made of PEBA foam with a 4mm offset, really feels like a zero-drop shoe. Set the shoe at 8mm, and the runner feels more poised and positioned for speed. In total, we made no less than 30 unique prototypes before we locked-in on a suitable combination. Not included or counted are the daily pattern and material tweaks that occur during normal shoe development.