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.
- 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)|
|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.
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.
The hood is well insulated, easy to use and comfortable.
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.
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.
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.