The Castelli Pro Mesh is a base layer short sleeve is a shirt you can use in various weather conditions. It keeps you dry in cold to mild weather conditions. And if you're going to cycle in freezing temperatures, you can wear it under the Castelli Flanders undershirt. And when it's warmer, and you open the zipper of your cycling shirt, you'll see the beautiful graphic print on this undershirt. The Castelli Pro Mesh is an ideal undershirt with short sleeves!