Like it's colder range sibling, the Castelli Alpha RoS 2 Light Jacket leverages the undeniable capabilities and properties of GORE-TEX INFINIUM™ WINDSTOPPER® 150 fabric, but changes the suggested temperature and makes the piece lighter by opting for using it only the front facing surfaces, while tapping into their own Nano Flex Xtra Dry for the rear facing panels. It is an Alpha construction, so there two distinct, but partially connected layers, and instead of the 3D grid-like fleece thermal layer on the colder range of the standard RoS 2, an inner layer of Castelli's light thermal ProSecco Strada fabric is used for it;s impressive moisture and thermal management. Other details are different as well, but conceptually the Light version of the Alpha ROS 2 is functionally a close match, but one built with flexibility, protection and comfort for serious riding and training in temps from 45°-69° F.

This jacket is about the art of dressing just right for cool conditions. You know those days when you need some protection from the cool air and/or a light precipitation, but not enough to bring out the winter jacket. Overdress and you'll be sweating and get cold because you're wet. Under dress and you never fully warm up to enjoy the ride. Sometimes that can be accommodated by layering, but one can only stow so many things in rear pockets and frankly if you can accomplish gearing up with two layers instead of five, life and laundry gets easier.

The concepts behind the construction are fairly simple: wind protection on front-facing surfaces, highly breathable fabrics on back-facing surfaces, and all-around water repellency in case you get a few drops of rain. But what makes this jacket spectacular is how Castelli executed these simple concepts. The wind protection comes from the GORE-TEX INFINIUM™ WINDSTOPPER® 150, lightweight two-way-stretch fabric that moves with you while being so light you'll hardly notice it's there. This light wind layer is backed by a separate ProSecco Strada inner layer with a separate zip that can be opened independently for perfect ventilation control. The back is made from Castelli Nano Flex Xtra Dry fabric that provides a good level of insulation yet has no membrane so allows for ample amounts of sweat to escape. The fit is close to body so there is no fabric flapping around, while the little details make the difference: easy-sliding YKK° zippers, reflective drain holes on the pockets, a lie-flat silicone gripper band around the waist.