Lightweight and highly breathable, the Mountain Hardwear Energy Tank features a fast-drying Koolknit polyester fabric treated with a wicking finish and rated with a 35 UPF. It's an excellent warm weather top for hiking, climbing and backpacking, especially if you're headed for spaces where shade is scarce. The tapered performance cut hugs your torso, helping dab moisture away from your skin to keep you cooler than any pullover made with cotton fibers.