When you're in the middle of a hot, slow climb you always wish it were cooler, and when you're descending from a nippy, blustery summit you're already taking it back. If you're trying to leave the layers at home and find one piece with the perfect balance of breathability and warmth for every part of your ride, grab the Patagonia Nine Trails Bike Jersey. It's made of a soft and lightweight fabric that not only delivers next-to-skin comfort, but breathes, wicks, and stretches while you're on the bike. The three-quarter length sleeves give you a perfect balance for rides that vary in terrain and elevation--breathability for the way up and coverage and warmth for the way down. Plus, they cover your elbows when you're wearing pads so you don't have to worry about uncomfortable gaps as you focus on the next hairpin turn. The articulated seaming and longer back hem give you a fit that's contoured to your posture and stance on a bike, and use flatlock seams to reduce chafing and discomfort as you ride. Meanwhile, a small zippered pocket keeps energy gels stashed close by, while Polygiene odor-control technology keeps your jersey fresh after leg-burning rides.