Marmot Trestle 15. Its kinda light. 4lbs. Compresses enough to get it into a 60l backpack. Or get a Deuter Dreamlight and SOl Escape bivy. You really dont have many options for a winter backpacking sleeping bag. The Dueter Dreamlite 500 weighs 1lb 20z. Its good for 45 degrees if you are a warm sleeper. Then add the Sol Escape. Then Warm some warm clothes and you might have a 30 degree sleep system