Shed Grams. Go Adventure. The trim-fit men's PROTON LT is Arc'teryx super-light, synthetically insulated hoody-jacket that's exceptionally breathable. It's designed to perform as a mid layer under a shell during cold ski days, and for wear as a comfortable outer during hiking or climbing trips. Fortius Air 40 outer fabric effectively balances wind- and- water-resistance with air permeability. Coreloft Continuous 65 insulation pads this jacket, providing consistent warmth. A No-Slip Zip prevents the front zipper from self-opening during activities. Dual hem adjusters stop cold drafts from working their way into your core. Arc'teryx also equipped this jacket with an insulated, helmet-compatible hood that adjusts for optimal protection. Insulated front pockets keep your hands warm and dual zippered chest pockets serve as storage sports for your phone and map.