I just bought this bag for my wife. I have had one myself for 5 years. I used it on an Aconcagua climb (sleeping at 19,800ish), and have used it on other climbs and several winter camping trips in northern Minnesota.

The bag is very warm. I recommend the Long size for my height (6'2") so you have enough room to stretch your toes. It has good space in your torso area so you don't feel restricted in it.I chose this bag over the Marmot CWM (-40 bag) because it's significantly lighter, and if it's really really cold out you just wear more clothes to bed.

The owner of the climbing guide company I've used, Phil Erschler, told me he uses that bag everywhere in the world, from Everest to Vinson in Antarctica. He said on Everest at high camp maybe he sleeps in his down suit too. But I agree with his opinion that the weight/space savings of this bag over the CWM make a lot of sense.

I love the bag and would recommend it to anyone. Worth every penny when you're sleeping somewhere cold.

I BOUGHT ONE AND TRIED IT OUT IN GRAIG CO. IN FEB 2009 , IT WAS ABOUT -25 OUTSIDE REAL WINDY WE WERE INSIDE UNCLE
BOB'S CAMPER HAD THE HEAT ON FULL BLAST ALL NIGHT 75-F ,SO I PUT ON HEAVY FLEECE PANTS AND SHIRT DOWN BOOTS AND THICK HAT . THE BAG ALL ZIPPED UP WAS SOMEWHAT WARM. I SHOULD HAVE USED A DOWN SUIT IN SIDE THE BAG . VERY GOOD
BAG THE - 20 VERSION

I got this for my wife to use because she gets cold easy. It is super compressible and lightweight. Marmot knows what they're doing.

I love this bag so much! After camping in a lean-to last winter in -15 degrees Fahrenheit weather I was sold. Having to take of layers when its that cold is so nice. The hood has plenty of room and the pouch hear the hood is a nice touch. this bag is great and defiantly worth the money

Wow this bag is a best thing you can have.if its winter and cold tuck yourself in and you will sleep like a baby.For hot nights just use it as base to lay on and get the extra comfort.Bit big in size so won't suggest it for backpacking

I love this bag! This bag kept me amazingly toasty on a winter backpack trip. After my first night in this bag I slept so well I couldn't wait for bedtime the next night just to get my bod into this awesome bag! I used a medium compression bag and got this bag about as small as a beach ball. Worth every penny!

I have used this bag at -25c and stayed nice and warm with the exception of my toes ( a little cool) very good loft and packs small. I love this sleeping bag. not much down on the bottom of this bag so make sure you have some good insulation under you.

Although this is a winter bag i just got done camping for 6 days in moab and it still worked fine, just slept with it open and around me and it is amazing . For winter trips though it is pretty Superior to most. When zipped up with the draft collar properly snug it becomes a toaster.

Excellent warmth, roomy to keep extra gear like boot liners and water bottles. You can tell this bag will last, the stitching/finish is high quality.

This is an excellent bag. My friend who was 6'6" said it was a little small for him and he was using the long. Also it is definitely too warm for year round any conditions weather. If you sleep with it unzipped than you should be ok in warmer conditions, but other wise this is a excellent winter bag.

Nice, warm, super puffy down bag. Haven't pushed the -20 limit, but at 10 above I had to open the zipper. Quality materials and a good zipper that even I haven't managed to screw up. I fit mine in a granite gear size large compression bag and it makes it a nice, rock hard size. http://www.backcountry.com/store/GRG0005/Granite-Gear-Round-Rock-Solid-Compression-Sack.html Good setup.

buy this bag end of story
where this bag distinguisned its self is when my old bivy failed leaked like a sieve in 33 deg rain then the temp plunged latter on that evining the bag iced up some but very little and my body heat disipated most of the moisture at no time was the goose down compromised at no time was I uncomfortable i diddent evin know the bivy was leaking untill morning
this could have been a survival situation
its a thin line between a cool adventure and a real nightmare
scottflues

I spent the night on my buddies apartment room floor the other night and this thing kept me so warm I was sweeting. It was however around 72 degrees inside. The night after though I spent above treeline on a 14er in the winter. It was about -25 outside and I slept like a baby in nothing but my boxers. Plenty of room for my waterbottles and clothes in the sack. A really really great, warm bag. Nothing beats marmots down!