The Western Mountaineering UltraLite is the lightest & warmest 20 degree bag I've ever experienced. At 1lb 12oz & 850 fill, this long version sleeping bag stuffs into the smallest stuff sack for maximum compactness. However I've recently been stuffing it into my day pack with all my other down items & clothes, etc. This package fits neatly into the bottom of my pack without compressing the down as much as other methods. I don't like using compression stuff sacks for 850 like I used to for 550 & 600. Just a personal thing. I'm 6' 3" 180 lbs. with plenty of room to spare in the WM Ultralite. No half zip here. Full zip for maximum ventilation & roomy foot box. In my opinion, Western Mountaineering is the best sleeping bag made, bar none!!!