This bag packs down tiny, and lofts up huge. This bag is often the envy of others.
Combined with the Alpinist bivy this bag has always kept me comfortable, it has been on so many adventures; at least 80 days of spring ski trips and still it lofts up and is ready to keep me warm.

I used this bag 5 consecutive nights in temps from 28 to 12 degrees F (in tent, on snow), slept comfortable to 25, woke up cool at 20 and needed to wear down coat, booties, etc at 15. No neck collar and the zipper does grab material sometimes but releases easily. If you want the Helium, get the EQ model with a less permeable outer fabric... better chance of reaching the temp rating. Still, I wish it had a down collar for temps below freezing. I'm replacing this Helium with a Western Mountaineering Versalite as I do have other WM bags and trust the temp ratings. BTW, the Helium is sewn in China and stuffed in the USA making it quite competitive in price.

Absolutely great bag. I was in the Linville Gorge, near Shortoff Mountain and camping at about 4,000ft of elevation, temps around 25 degrees and 60mph winds which made it feel in the low teens. Bag was awesome, I was sweating in it while just wearing sweat pants and a t-shirt. Bought a compression sack for it and the bag can be brought down to the size of a football.

I took this on a trip to the Sawtooths in May for some backpacking/ski touring and car camping. I woke up sweaty on a 19 degree morning with my bag unzipped all the way. Wow! I was using a foam pad on dry ground. I was just right on a 15 degree morning on the snow. I'm a somewhat warm sleeper. I'm 6' and the regular seems to fit just right. The shell kept the heavy frost out. The bag packs down fairly small. I love this bag and my Marmot Atom also. The Helium has a stiffer shell and a little more room inside than the Atom.

Awesome bag. Seriously, one of the lightest bags on the market, as well as one of the most comfortable I've been in. Get a compression sack to go with this bag though, the stuff sack it comes with is super thin and seems like it would tear easily. All in all, a great product.

I've had this bag for about a year. I consider myself an average sleeper for warmth and would rate it comfy at ~25F with long underwear.

Positives: light weight for the warmth- the long weighs 2lb 4oz in a 1 oz silnylon sack. Great construction like all marmot gear.

Negatives: no draft collar. IMO this is a bad omission as this one ounce addition can easily add 10F of warmth; I can feel the heat escaping across my upper chest. The cut is too big, esp from the waist up. You could fit a 300 pounder in this thing and I don't see too many 300 pounders backpacking :)

Summary: make the cut a bit smaller and add a draft collar; it would be both lighter and warmer and fit 99.9%

i just put this bag at the bottom of my backpack (not in the stuff sack) under 2lbs and 15 degrees is simply magic. i'm a cold sleeper and slept in nights down to 35 and it was plenty warm for me. the feel of the bag is luxurious and lofts great. it doesnt feel cheap at all. i highly recommend it.

Compared this bag to my 0F Mountain Hardwear Phantom bag. Obviously it is a 1lb lighter and less warm as a result. I appreciated the lightness on a recent spring skiing trip where overnight temperatures were down to around 20F. Overall it is a great bag. Seemed a little more roomy though than my Mountain Hardwear, which took longer to warm up. Also I missed the baffles around the neck - found myself pulling the hood and the neck draw string tighter as a result. I am 6 ft / 195 lbs and went with the long, mostly so I could put my boot liners, a hot SIG bottle and my wet gloves (around the SIG bottle) at the bottom.

Like staying warm at night? Light weight? Packable? After hiking/ biking/ paddling/ portaging all day- I just want some comfortable sleep so I can get up and do it again. Kept me warm with nothing more than the tent and it's footprint- no therma rest required (for heat retention at least) Pricey? You bet, but it's gonna last a long time and you're gonna sleep like a baby. Don't skimp on you're sleep comfort- you'll wake up a happier person in the morning and you'll probably thank those wonderful people at marmot when your friends are complaining about how they froze last night (or how heavy their bag is).

Hands down, this is the best bag in my arsenal. Make certain you use it for the temperature it's designed for. Not a bag for 35 F or warmer. Packs down tight and light, also finds its loft real quick with a toss of the hand. This bag is so comfy you'll end up taking it when it's 45 F and you'll sweat all over the place so i'd recommend a liner.

This is an excellent bag for the money. It reaches its temperature rating easily if used in a bivy bag. That way you can use the regular Helium and not get wet. We slept under a fly,in bivy sacks on shorty thermarests down to minus 10 C. No problem. I love the way it compresses. This Fall we'll try it while elk hunting when pack space is at a premium. My scale might be wrong but I think it weighs about 1.5 kilos but that is still better than any other bag I have tried. I find it roomy too (I'm 5'11" and 170 lbs)
Durability remains to be seen but I think it's the answer for me.

just used it for a trip in Patagonia, temperatures went down to 32F at night, I slept in one layer of underwear just perfect warm. One night started at 65F, thanks to the long opening zipper, I fell asleep without sweating. Fantastic for that weight and size.

I purchased a Helium 15 degree for a September hike of the John Muir Trail. Night temps varied but lows in the high 20s at higher elevations. The bag was more than adequate and on a couple of the colder nights I swapped with my hiking partner who was sleeping cold in another top name 20 degree bag. I agree with some of the comments that suggested a neck draft collar would improve the bag. I also found that the zipper seemed inferior for this high end bag. It snagged easily and though it was also easy to free, having to do this multiple times to get the bag zipped was frustrating. Whatever weight was saved with this zipper was not worth the inconvenience. Marmot should fix this.

This bag is one of the Best bags out on the market! Just put it between your hands and push your hands together and you will see! and then do the same with other brand bags. Helium is the way to go! The Best part it keeps you Warm Too! and condensation rolls off of it! Buy it you can't go wrong! Super lite ! packs small in Marmot bag but it needs to come with a extra small compression sack would have pack smaller!

I got this sleeping bag (okay, my mom got it for my birthday!) for my hike on the John Muir Trail. It was less than half the weight of my old sleeping bag, and MAN was it toasty!

We had a freak cold-snap up in Tuolumne, and the temperature went below freezing several nights--we even had some hail in August! But unlike my buddies, who went to bed wearing every layer they owned, I was sweltering. I never had to keep it zipped up on even the coldest night.

On the minus side:
-It is pricey.
-The zipper is a bit annoying.

Plus or minus:
-For a 5'8" guy, it's perhaps a bit too large. I had lots of room to roll around in.

If you can afford it, it's worth a splurge.