User Review: Marmot Women's Helium
Design: left zip mummy
I have primarily used this bag in northern summers, as an all purpose bag. I have spent two summers of trip leading sleeping it it all summer in Maine and Wisconsin/Minnesota, while also pushed its limits in October in northern MN and January in the Grand Canyon. I recently got a Sea to Sumit 8L dry sack for it, which it fits in perfectly. These bags are not submersible, and take the place of the garbage-bag-in-a-stuff-sack combo in my pack.
The only time I've ever felt the cold in this bag was through my ground pad when I needed something more than a short 3-season Therm-a-rest. My last night in the Grand Canyon I slept out under the stars and had ice form on the top of my bag and didn't know it until I crawled out in the morning.
Most recently I stuffed this bag inside my zero degree bag and slept out in -15 degree weather and stayed warm.