In my search for the lightest and best bag for sheep hunts, I came across Western Mounaineering. I was previously set on a Marmot Helium, but the Western Mountaineering bags look equal or better. Their 10 degree bag is listed as only 1oz more than the 15 degree Helium, and their 20 degree bag is lighter. Is all else equal with these products, or am I missing something I should be comparing? They are listed as equal sizes. How about outer material qualities?