Midway up the final scramble of the unofficial Mount Tam Hill Climb, with lungs burning and quads screaming, nobody’s thinking about evaporative heat loss or air permeability. The Fore Runner takes care of it, thanks to an ultralight, highly breathable and fast-wicking 100% polyester fabric. Meanwhile, flatlock seams (offset at shoulder) provide no-chafe, next-to-skin comfort, and a locker loop lets you dry it out afterward. The running shirt’s updated sleeve design is now more streamlined, with a range-of-motion-enhancing underarm gusset that comes in handy at the finish line–when you reach up and touch the door of the Tamalpais lookout tower. With 15-UPF sun protection, Polygiene permanent odor control and reflective logos on the chest and center back neck.