User Review: Marmot Men's Helium
Fill: 900 fill down (that's what the tag says)
Temperature Rating: 0F, -18C
Weight: 2lbs ~ 900g
Price Paid: $379 USD
I'm on my third winter with the Helium. It's a great bag for sub-freezing nights, but much too warm for warmer autumn temps. I use a lighter synthetic bag (Kelty Lightyear 3D) for warmer nights in damp weather.
My coldest night so far in the Helium was 10F (-12C) and wearing only briefs and t-shirt I experienced no cold spots even rolling around a bit. I'm sure I could manage sub-zero temps in the Helium wearing mid-weight thermals or microfleece. The hood can be cinched down to a small breathing portal if you're not claustrophobic. The cinch cords and zips can take a bit of dexterity to undo, but hey...what's the hurry on a cold morning?
Overall, I think the Marmot Helium is a serious moderate cold weather bag true to its temperature rating, light, small in your pack, and worth the premium price.