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Nuclear physics meets camping.

Deep under Utah's Wasatch Mountains, there's a secret gear lab where smarter-than-NASA scientists shoot feathers, fabrics, and waterproof treatments around a track at millions of miles per hour, crashing them together and observing the products that result. One of the creations is the Marmot Atom 40-Degree Down Sleeping Bag, which spontaneously sprang into being when a gaggle of 850-fill goose down collided with some light and durable Pertex Microlight fabric, right before the whole thing smashed into a DWR coating and Down Defender water-repellent treatment.

Once the scientists were able to conduct tests and confirm that the package was suitable for serious outdoor use in mild conditions, and that no new black holes had been created, the Atom was ready to be seen by the public. It's been drawing the most interest from backpackers and campers who like to go ultralight during the summer months, and during recent study, independent researchers have discovered a Nautilus six-baffle hood, insulated draft tube, and stretchy baffles around the head and feet, which seem to allow for comfortable movement during sleep. The Atom has also led to speculation that, contrary to previous understanding, zippers and zipper guards were created in the initial microseconds of the universe's existence.

  • Ultralight summer camping bag
  • 850-fill down with Down Defender water-resistant treatment
  • Mummy bag with sewn-through baffles
  • Pertex Microlight nylon ripstop fabric with DWR treatment
  • Ultralight
  • Six-baffle Nautilus drawcord hood with insulated collar and draft tube
  • Trapezoidal footbox construction
  • Stretch tricot baffles and head and foot
  • Stuff and storage sack included

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Here's what others have to say...


Perfect summer bag

  • Familiarity:I've used it several times

Prior to purchasing this bag I used my 20 degree bag for everything. After many nights of waking up soaking wet, I cracked. Since getting this bag I have been very comfortable, even damp nights down in the 30's. Bag packs down very small in the compression bag, yet is easy to regain the loft. Love it!


Solid bag

  • Familiarity:I've put it through the wringer

Simple mummy construction and high quality down never go out of style. I found it true to it's rating as I'm a cold sleeper and was fine down to about 48 degrees but with a fleece layer was comfortable to 40 sleeping on a small zlite foam pad.

My only complaints are that the zipper snags a lot due to the lightly filed draft tube and I would have preferred shock cord for the hood cinch(totally personal preference).

In terms of fit, I'm 6'2" and 150lb and the tall fits me with room to spare in both height and width(would love a slim size!).

The dwr finish held up admirably when my tarp started leaking in heavy rain and the treated down allowed for quick drying with only body heat the next night in a shelter.

In all, a great summer bag for ultralight backpacking!


Excellent Product

  • Familiarity:I've put it through the wringer

I bought a Marmot Atom 40 degree down sleeping bag to mate up to an Exped DownMat 7 LW inflatable sleeping pad for my sleep system . The Atom has continuous baffles, so I can move all the down up top and use it more like a quilt for cold weather. My 20-inch wide foam Ridgerest wasn't keeping me warm enough and I was waking up at around 3 or 4 in the morning. The combo worked great on a section hike of the Appalachian Trail in the Smokey Mountains. The Atom is rather wide in the shoulders and spilled over the sides of the Ridgerest. The long/wide version of the DownMat fixed that problem. I love the silky smooth material and the drawstring hood works and fits like a charm.