Dayhikes, overnights, mountain bike rides, ski tours—if we were sweating, we wanted this breathable top. It’s made of 56 percent merino wool, with mesh and perforations in key areas across the back and sleeves, which helped us dump heat fast. (The 44 percent polyester helps it dry quickly when it does wet out.) Beyond that, it’s all about the fit: The Merino Sport 150 Short Sleeve is more flowy than a typical shirt, which our testers appreciated for air circulation and not being too constrictive when worn under a pack. (Note: Size down if you want a closer fit.) (w’s M); w’s XS-XL;