November 20, 2015 8:16 PM MST - Subscription purchasing, account maintenance, forum profile maintenance, new account registration, and forum posting have been disabled
as we prepare our databases for the final migration to our new server next week. Stay tuned here for more details.
Subscribe Contribute Advertise Facebook Twitter Instagram Forums Newsletter

Marmot Atom Sleeping Bag REVIEW

A one pound, three-season bag with top quality materials.

Overall Rating: Above Average

The Marmot Atom is a darn good bag – light, nice price and good materials. But it doesn’t quite push the envelope. It will need baffles at a similar weight, or a couple of ounces less weight - without losing warmth - to move up a notch.

About This Rating

Print Jump to Reader Comments

by Don Wilson |

Marmot Atom Sleeping Bag REVIEW


The Marmot Atom sleeping bag is a one pound bag with high quality 850+ down fill and a Pertex Quantum shell – all top notch specifications. It has a half zipper, a nicely contoured hood, 4 inches of specified loft and is rated by Marmot to 40º Fahrenheit. It comes in a regular length (fits to 6 feet) and a long length (fits to 6 feet 6 inches). The Atom slips nicely into the niche of 1 pound mummy bags – but is it near the top of the pack? I did most of my testing over the course of the winter in the desert southwest, in conditions similar to alpine summers; perfect conditions for pushing the Atom near and beyond its limits. The photo at right was taken on a cool winter night in Sabino Canyon, Arizona.

The Atom is the lightest member of Marmot’s 850+ series of sleeping bags, which also includes the Hydrogen (1 pound 5 ounces), Helium (1 pound 13 ounces), Helium EQ (2 pounds 3 ounces, waterproof/breathable shell), and a women’s version of the Helium (1 pound 13 ounces, to 5 feet 6 inches). All except the Helium EQ feature similar specifications – same down, same Pertex Quantum shell.

What’s Good

  • Comfortable and breathable shell fabric
  • Hood is warm, comfortable and easy to use
  • At close to 1 pound, a very light three season bag
  • Good value for your dollar

What’s Not So Good

  • Over 2 ounces above specified weight
  • Some cold spots due to construction and fill



2006 Marmot Atom Sleeping Bag


Mummy (with half length (38 in, 97 cm) zipper)


850+ down

  Measured Loft

1.9 in (4.8 cm) single layer loft averaged from measurements taken at the shoulder, hip and 16 in (41 cm) above the footbox. Baffles above the zipper are continuous to allow loft to be adjusted by the user

  Manufacturer Claimed Temperature Rating

40 ºF (4.4 ºC)


1 lb 6.6 oz (640 g) long length as measured. Stuff sack adds 1.3 oz (37 g). Manufacturer’s spec 1 lb 0 oz (454 g), size regular, 1 lb 4 oz (567 g) size long


Regular (to 6 ft, 1.82 m), Long (to 6 ft 6 in, 1.98 m)


Pertex Quantum N-090 ripstop shell Pertex Quantum N-090 taffeta lining


Insulated draft tube, half length zipper, zipper guards, draw cord and hood, 5 in (13 cm) spacing, sewn-through construction, stuff sack and storage sack included


$249 (Regular), $269 (Long)


The Atom is a narrow mummy bag and with its 40º temperature rating from Marmot, is clearly targeted at the ultralight summer backcountry traveler. My test bag is a size long, which has a specified weight of 1 pound 4 ounces. I was disappointed that the bag came in at 1 pound 6.6 ounces. The measured loft is 1.9 inches (single layer), just under the manufacturer’s specified loft of 2 inches (single layer). The Atom has sewn-through construction, with seams spaced 5 inches apart. Below the zipper, the down compartments are blocked, but above the zipper the compartments wrap around from top to bottom. This allows the user to move some down between top and bottom if necessary. The Atom has a mummy cut, with 62 inches of girth at the shoulders, 58 inches at the hip and 40 inches at the foot. That makes the Atom a little more roomy than some other ultralight bags, and I enjoyed the extra room on long winter nights. If tight mummy bags drive you crazy, the Atom is worth a look as an ultralight option.

Marmot Atom Sleeping Bag REVIEW - 2
The Marmot Atom has a 38 inch long half zipper which provides easy entry and exit, but less temperature control than a full zipper. The size long bag is cut plenty long for those up to 6 feet 6 inches tall.

One of the nicest features of the Atom is the hood. It is roomy, well insulated, nicely contoured to reduce cold spots, and very easy to adjust. I have spent several nights cocooned comfortably in the hood for 12 hours or more. Most of my testing occurred in dry conditions – not the best for testing the breathability of the Pertex Quantum shell. But I was always dry and comfortable and I expect the shell material will prove to be more breathable than shells on most comparable bags. I experienced absolutely no down leakage over a few months of testing. I would have expected a little leakage in a new bag. Another positive feature of the Atom is the price. The regular length model goes for $249, while the long comes in at $269. That compares quite well with similar bags that push the 1 pound envelope, such as the Western Mountaineering Summerlite.

Marmot Atom Sleeping Bag REVIEW - 3
The hood is well insulated, easy to use and comfortable.

Marmot Atom Sleeping Bag REVIEW - 4
The Atom has a zipper guard (stiffened lining on lower side in black) to reduce fabric snags and a moderately stuffed draft tube to reduce cold spots along the zipper.

Marmot Atom Sleeping Bag REVIEW - 5
The Atom uses sewn through construction, with seams placed at 5 inch intervals. The least insulated part of the bag is around your legs, which resulted in some notable cool spots when using the bag on cool nights. I measured the maximum loft of the Atom at just under 2 inches for a single layer (1.9 inches averaged from three locations). The sewn through construction reduces the effective loft below the measured maximum loft.

Missing from this review (and for all sleeping bag reviews published here, for that matter) will be an assessment of whether or not the sleeping bag performs adequately at temperatures near its manufacturer-reported temperature rating. Click here for the complete Backpacking Light Position Statement on Sleeping Bag Temperature Ratings.

What’s Unique

The Atom has excellent specifications and material quality. The down fill, Pertex Quantum shell and specified weight are a good combination and make the Marmot Atom a very good choice for a summer bag – especially at its price ($249 for size regular).

Recommendations for Improvement

My biggest disappointment was that the Atom weighed 2.6 ounces more than the manufacturer’s specified weight (the test bag is a size long). It seems likely that the regular size bag will also weigh in at least a couple of ounces more than its specified weight of 16 ounces. To really be cutting edge, the Atom will need to shed a couple of ounces, or retain its current weight and add ultralight baffles to improve its effective loft and warmth.


"Marmot Atom Sleeping Bag REVIEW," by Don Wilson. (ISSN 1537-0364)., 2007-03-20 03:00:00-06.


Reader Comments

You must login to post comments.

New Visitors: Create a new account
Remember my login info.

Marmot Atom Sleeping Bag REVIEW
Display Avatars
Sort By:
Benjamin Smith
(bugbomb) - F - M

Locale: South Texas
Marmot Atom Sleeping Bag REVIEW on 03/20/2007 23:24:00 MDT Print View

Companion forum thread to:

Marmot Atom Sleeping Bag REVIEW

Chad Mason

Locale: Arizona
My Atom is overweight as well... on 03/21/2007 08:47:49 MDT Print View

I recently purchased an Atom - regular length. It weighs in at 1 lb 3 oz and a little over 20 ounces including the stuff sack. I, also, am a little disappointed in the extra weight.

Steve .
(pappekak) - F

Locale: Tralfamadore
Re: My Atom is overweight as well... on 03/21/2007 09:26:05 MDT Print View

Since the Atom has a partial zipper vs. the Western Mountaineering Summerlite, the Summerlite is fully baffled vs Atom's sewn through construction, and the two bags have about the same loft I wonder where the weight difference is? Is it the Atom's fabric or a lower grade down?

Don's measurements of the Marmot Atom and the Western Mountaineerig Summerlite:

weight advertised: 1lb 4oz
weight measured: 1lb 6.6oz
loft (single layer shoulder & hip): 1.9 in
loft (above footbox): 16 in
fabric: Pertex Quantum N-090 ripstop shell Pertex Quantum N-090 taffeta lining

weight advertised: 1lb 3oz
weight measured: 1lb 5.4oz
loft (single layer): 2.1 in
loft (double layer shoulder & hip): 4.1 in
loft (above footbox): 16 in
fabric: 0.9 oz/yd2 (31 g/m2) Extremelite 20D nylon shell

Summerlite Review:

Edited by pappekak on 03/21/2007 09:40:02 MDT.

Don Wilson
(don) - MLife

Locale: Koyukuk River, Alaska
Re: Re: My Atom is overweight as well... on 03/21/2007 17:10:21 MDT Print View

Well, I can't say for sure without cutting up my bags (and that is NOT going to happen - not even for BPL!).

I believe the lighter weight of the Summerlite comes mainly from a combination of shell fabric and down. And remember the difference in weight is only a little more than an ounce in the size large.

I think both bags have high quality down - but I wouldn't be surprised if the Summerlite has less down than the Atom, even though it has higher average loft. The baffles add cost and complexity to the Summerlite. But I think they also allow the down to loft more consistently, and hence may allow a bag with less down to have a higher average loft. I think this may be particularly important in very light bags such as the Atom and Summerlite. The baffles improve the ability of the down to be effective for the least amount of weight.

James Pitts
(jjpitts) - F

Locale: Midwest US
Re: Marmot Atom Sleeping Bag REVIEW on 03/22/2007 20:31:58 MDT Print View

This is a great sleeping bag... it is what it is... a sewn-through down bag. That means it is less expensive and has limitations. The extra weight is a disappointment. I'll weight mine and post the results.

Johnathan White
(johnatha1) - F

Locale: PNW
Marmot Atom Sleeping Bag REVIEW on 03/22/2007 21:15:18 MDT Print View

This has been one of my favorite bags. The hood on it cannot be beat IMHO. I have had it down without any base layers to 40F and with light base layers to 36F. Mine weighs in at 18.6oz for the regular. I could cut tags, shorten sinch cord length but at 18.6 oz, why bother. Another great feature is the 62" girth. You can layer a bit under it and not feel too cramped.

Edited by johnatha1 on 03/22/2007 21:20:25 MDT.

Glenn Roberts
(garkjr) - F

Locale: Southwestern Ohio
Re: Marmot Atom Sleeping Bag REVIEW on 03/23/2007 05:15:12 MDT Print View

Earlier, Steve asked why, with the extra features (full zip, baffles, etc.), the WM Summerlite weighed less than the Atom. The shell material and down (quality and/or quantity) could be part of it, but the cut of the bag could also be a culprit.

Reading the specs, it appears that the WM is a slimmer fit than the Atom. I don't own either the Atom or Summerlite bag, but I know from crawling into the Marmot Hydrogen and Helium in the shop that they are roomier than most of the comparable WM bags. I prefer the WM bags to the Marmot, if they fit; if they didn't, Marmot would be my first alternate. (For what it's worth, I ended up with the WM Mitylite and Megalite; the other bags I tried in the Extremelite series were cut too tight for me.)

Edited by garkjr on 03/23/2007 10:33:47 MDT.

Don Wilson
(don) - MLife

Locale: Koyukuk River, Alaska
Re: Re: Marmot Atom Sleeping Bag REVIEW on 03/23/2007 13:24:15 MDT Print View

Very good point Glenn. Certainly the different cut plays a big role in the relative weight of the Summerlite and the Atom.

Based on the comments so far, it looks like Atoms are generally coming in about 2.5 ounces above the specified weight in both regular and long lengths. I think Marmot would be much better off with a more accurate spec weight - thereby not dissappointing weight conscious buyers.

Michele Mason
(bianchilvr) - MLife
Article Description Doesn't Match Content on 03/23/2007 14:15:18 MDT Print View

As I own an Atom, I think the review here on BPL is right on.

However, my email concerning this article contained the following description:

Marmot Atom Sleeping Bag REVIEW

Backpacking Light staff discuss how to get the most out of any winter
trip from day trips to multi-day expeditions.

I eagerly clicked the link to read how the author used the Atom for winter trips, and I really don't see this type of information contained in the article.

For the record (since it is a complaint of mine, too, but my Helium suffers the same weight difference from the published weight), my Atom is 18.5 oz for the regular length.

Edited by bianchilvr on 03/23/2007 14:24:31 MDT.

Don Wilson
(don) - MLife

Locale: Koyukuk River, Alaska
Re: Article Description Doesn't Match Content on 03/23/2007 16:45:00 MDT Print View

Michele -

Yes, we had a blooper in the email this week. Sorry about that. We do have more coverage planned regarding winter outings - just not last week.


Benjamin Smith
(bugbomb) - F - M

Locale: South Texas
Re: Article Description Doesn't Match Content on 03/23/2007 21:21:01 MDT Print View

Yep, Michele, you caught us! Stay tuned for the winter article referenced in that tantalizing description - it should be coming within the next week or two.

Michele Mason
(bianchilvr) - MLife
Looking Forward to "Part II" on 03/24/2007 10:06:17 MDT Print View

Unusual, i.e., not mainstream techniques, interest me most--my fav article was the one on hiking in sustained, cold rain a few months ago.

I can't wait to see what y'all come up with on this one!