Craft Pro Zero Extreme was first designed for the Swedish Nat'l Nordic Skiing team. In the early and late season, they often skied in cool conditions where they were generating enormous body heat through intense efforts. They needed a base layer that would trap in warmth when they were skiing at a moderate pace, but that could wick and vent like mad when their effort level was pegged. Hence, Pro Zero Extreme was born. Craft recommends its use for high-intensity rides from 25-55 degrees. It's perfect for early season intervals as well as cyclocross racing. It's with Pro Zero Extreme in mind that Craft chose to be the official apparel sponsor of the USGP of Cyclocross. Pro Zero Extreme is built with hexachannel Pro Cool fabric against your skin, identical to what you get in a summerweight Pro Cool base layer. This hexachannel layer is paired with Craft's hollow-channeled Thermolite fabric to help trap in body heat on cool days. It has a seamless torso, so a tight-fitting jersey won't cause your base layer to chew into your skin. Adding to the comfort is the fact that Craft has gone to what they call 3D cutting lines. You won't see any straight seams on the Pro Zero Extreme. The panels and seams are curved identically to the shape of a cyclist reaching for the handlebars. Available in Black in sizes Small through XX-Large.