You're going to have a hard time finding a jacket that works more efficiently than the hybrid-constructed Icebreaker Men's Ellipse Half-Zip Hooded Insulated Jacket. The chest panel and hood are insulated with MerinoLOFT for serious warmth where you need it most, while the rest of the jacket is crafted from a soft merino wool blend that amps up breathability and moisture management while minimizing bulk. Stretch side panels offer increased mobility for ski touring or hikes through rugged terrain, and its slim fit helps the jacket fit comfortably underneath a shell when nasty winter weather approaches. Icebreaker compromised with half-length zipper that makes for easy on and off and lets you ventilate excess heat but is still more packable than jackets with full-length zips. It also has multiple zippered pockets so you can safely stash snacks, maps, keys, and other small necessities.