Vest from Arc'teryx. Atom Vest M is a lightweight, stretchy vest with a regular fit, designed for high-output activities and versatile use as a midlayer or standalone piece. The vest features lightweight, breathable Fortius™ Air 20 nylon with recycled content, stretch synthetic insulation that provides warmth without restricting movement, and stretch Octa® Fleece side panels that enhance ventilation and comfort. The vest includes an adjustable hem drawcord to block drafts and two zippered hand pockets.