Helium

Information on the bag:
The Marmot Helium Sleeping bag packs are smaller than a loaf of bread and take you down to 15 degrees. At a mere 2 pounds you have a super versatile 3 season ultralight sleeping bag. The Helium is certified 900 Fill Goose Down the best weight to warmth down in the market that is independently tested and certified by International Down and Feather Laboratory in Salt Lake City, Utah. The down-filled draft tube eliminates cold leaks through the zipper and the side blocked below end of zipper keeps the down evenly distributed. The foot box is the classic trapezoidal foot box for more room and warmth where needed. The hood uses a hood draw cord to keep you head snug and warm in freezing conditions. The Helium out shell is Pertex Quantum that is both soft and highly breathable. This a is must have bag.

Other Features:
Shell Material: Pertex Quantum N-090
Liner Material: Pertex Quantum N-090
Draft Collar: Yes
Fill: 850+ Degree down
Overall Weight: [Reg] 1 lb 13 oz [long] 2 lb
Length: [Reg] 6.0"" [long] 6.6""
Shape: Mummy
Stuff Size: [Reg] 7.5"" x 15"" [long] 7.5"" x 15""
Warranty: Lifetime
Use: Backpacking, camping 3 season

My Experience:
I took this bag because of its reviews online. It is considered one of the lightest of bags, with the most warmth to weight ratio. Yes, IT REALLY packs smaller than a loaf of bread, and, when, at first, you see its stuff sack you go - WHAT??? IS THIS GOING TO FIT IN THIS SACK???? - To everybody's amazement, it fits, although it takes a bit if pushing. On top of it, I recommend buying a compression sack (I bought one from REI) which even reduces the size.
I took this bag on Whitney last year, and I must say, it didn't dissapoint me AT ALL ! At night, it was really cold outside, but, inside the bag, I was toasty as ever. I had worn a fleece jacket though, but that was just partial preparation for the next day's summit attempt. I could have done without that as well.
One recommendation I would like to give Marmot is that it would be nice to have a Helium with right zipper, as I am right-handed. Sadly, this awesome bag comes only with a left zipper.
Overall, I would highly recommend it to anybody !

I got the woman's model because it was on sale and it is lighter, only 1 lb 10 oz. I am 5'7" so it fit fine. I used it for my whole PCT hike and was only chilly 2 nights, once in S. Cal. sleeping without a tent and woke up to a damp ice covered bag, the other time in Washington when the bag was a bit damp from daily rains. However with even minimal sun, it dried very quickly at lunch time or break time. The only problem I had with the bag was that I was often too hot and with only a half zipper it doesn't open up enough to cool off.

Light, small, warm - a home away from home!

...and light. I have used this bag for at least 100 nights and it still looks like new. I have used it extensively backpacking/peakbagging in Colorado mostly in the 3 seasons but also some winter. It is warm and comfy and AWESOME.