Rating: 5 / 5
I don't know if Marmot even makes this bag anymore because I haven't seen it in their recent catalogs. Maybe it's because of the name, which first brings to mind a bipolar medication rather than an element (like the Helium and Hydrogen)?
In any case, I love this sleeping bag. It's the only 0 degree bag I've found that's lightweight. And because of the 3/4 zip, it's perfect for winter, though it has made me feel a little claustrophobic and took a bit getting used to. However, being a cold-sleeping woman, it has been perfect in the summer at high altitudes -- it even got me through a 2-day snowstorm in the High Sierra.