The Squadra Stretch shell keeps the wind off on cool-weather rides or long descents, while the stretch panels keep the jacket fitting close to body and eliminate flapping fabric. This modern interpretation of the wind shell jacket is the one you keep in your pocket for a long descent or put on for the first hour of the ride until the day warms up. Castelli completely reimagined what the 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 allowed them to give 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. Castelli kept it very compact so that it can pack away into minimal space in a jersey pocket. The stretch panels are treated for water repellence, which will help in a light mist, but this is not meant to be a true rain jacket.