Arc'teryx Proton SL Hoody Men'sClimb comfortably in our lightest, most breathable fully insulated hoody. The Proton SL Hoody was previously the Proton Lightweight Hoody. The lightest, most breathable option in our Insulation Collection, the Proton SL Hoody takes the guesswork out of warming up on cold climbs and other high output activities in cool conditions. The knit insulation holds its loft and shapeno matter how often you stuff it into the bottom of your pack. More