It's everyone's dream—go from freezing temps to working up a sweat, no change in layers required. The Kor AirShell Warm Vest doesn't require shedding or adding layers thanks to a powerful combo: temperature-regulating AirMesh on the inside to keep you warm when it's cold and cool when it's warm, and breathable, stretchy Pertex Quantum Air on the outside to release clammy sweat. All while fending off pesky branches—no problem—as you pick up speed on cross-country trails.