Excellent Marmot Helium 15 Degree 850 Fill Down Sleeping Bag Reg Left Zip. The Marmot Helium Sleeping Bag is a down sleeping bag for backpacking and mountaineering in temps down to 15°F. Pack up for a week or more and get to exploring, knowing your back won’t be crying thanks to the low weight of this 2lbs 1oz bag. The 800+ fill power down is toasty warm, wrapping around you as you sleep, rejuvenating for the next day on the trails.