The Climate Long-Sleeve Shirt uses On ThermaTec(TM) construction and a woven, multidimensional fabric surface to hold warmth on cold runs while still wicking sweat as effort builds. A quarter-zip front vents heat on demand, and spiral dart elbow seams with a contoured back seam let the shirt move through a full stride without binding. What Our Gearhead(R) Experts Are Saying:"I started a 20-degree morning run fully zipped and never felt the chill that usually has me turning back early. By mile four I'd dropped the zipper halfway and stayed comfortable instead of overheating like I would in a heavier layer."