The Arc'teryx Women's Atom LT Jacket is the skinniest full-jacket member of the Arc'teryx Atom family, but don't let the sleek profile fool you. The Atom LT packs a wallop of warmth when mid-winter marathon training finds you outside pounding snow-packed pavement in Minot, North Dakota. And thanks to its trim fit, this slick little number also works well under a shell when the weather dictates more hardy protection. Coreloft 60 insulation leans towards the lighter side of the Coreloft cabal, and does not cover every inch of your upper body. Deliberate design puts the insulation where it matters most: your core, arms, and shoulders. Along the jacket's sides and under your arms, you'll find Polartec Power Stretch with Hardface technology. This four-way stretch fabric accommodates your every move, and Hardface technology ups the ante on abrasion resistance. The non-insulated panels also help the jacket breathe so you don't become the steaming carne asada inside a toasty synthetic insulation burrito. As with all members of the Atom family, the Atom LT can be shoved into its own sleeve for packing efficiency and economy of size when space is a premium. The DWR coating fortifies the water-repelling aspect of the shell fabric, while the air-permeable polyurethane layer enhances the shell's wind resistance. Articulated elbows and underarm gussets give your arms free range of motion whether you're dancing in the firelight or fighting for the final pitch. From dawn patrols to winter running to shoveling the driveway after a late March dump—whatever your preferred poison, the Atom LT will keep you warm through the bitter end.