This Castelli Squadra Stretch W Jacket is a modern interpretation of the wind shell jacket, otherwise known as the flimsy, loose-fitting one you've kept in your pocket for a long descent or put on for the first hour of the ride until the day warms up. That jacket used to be a simple affair, an essentially effective nylon shell, but the lack of stretch meant that it had to be cut on the generous side to fit all body shapes, both on and off the bike.

The design team at Castelli completely reimagined what a shell jacket should be and how it's constructed. They added panels on the sides and the sleeves in a very high-stretch yet tightly knit fabric that gives the jacket a modern, close-to-body fit for aero gains on any terrain, and it actually keeps more heat in than a jacket that's flapping about. It was kept very compact so that it can pack away into minimal space in a jersey pocket. The stretch panels are treated for water repellency, which will help in a light mist, but this is not meant to be a true rain jacket. The collar is tall to keep cool air out, and Castelli adds reflective details on the chest and lower back for low-light visibility.