The thermal jersey is the first step into cool-weather clothing, where Castelli has set the standard for what clothing can do. We've carried on that tradition here. You'll wear this jersey on cool days, so we've given it a brushed fleece backing but kept the fabric stretchy for a great fit. Since you're using it in conditions that aren't cold enough for a jacket, we've engineered the fabric to let some air in so you don't overheat. We think a jersey like this should be pure function, so you've got three spacious rear pockets, silicone gripper elastic, and an easy-sliding YKK® Vislon® zipper.