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Marmot Atom 40F Sleeping Bag: "Lightweight and designed for comfort"

With its incredibly lightweight design, the Marmot Atom sleeping bag is a backpacker's dream, so long as the weather is warm.

The mummy style design goes to great lengths to keep out the chill for nights when the cold does settle in.

    What's Smart?

  • Comfortable
  • Lightweight
  • Designed well
  • Durable

    What's Not?

  • Possible cold spots
Suitable for: Camping, Backpacking, Warmer Temperatures
Approx price: $289.00 - $309.00 US
Countries available: US - Canada - Europe (check with us or Marmot for others)

Features and Design

The style of this unit is designed to be used in moderate conditions. It is more focused on keeping you comfortable than keeping you warm. The exterior cloth is made of water resistant nylon with rip stop technology, while the inside is made of recycled polyester for a softer feel against the skin. Wearing some type of clothing while in the bag is still recommended.

The six chamber hood is designed to keep the baffling in place around your head to keep you warm. This design features only a down filled draft tube, rather than a collar, but the addition of the Velcro-free face muff will help keep the chill out of your bag while keeping the hood pull cord away from your face.

The half-length zipper stops above the hips, making the bag awkward for mating. The interior of the zipper is guarded, to prevent accidentally biting your arm in the zipper's teeth. However, the half zipper design makes it difficult to air out the bag should overheating become an issue during the night.

The extreme lightweight design makes this bag perfect for backpackers who are going to be in moderate weather. Car campers will also find the comfort and warmth of the design to meet their needs well.


With its 850 goose down fill, the Marmot Atom is among the lightest bags on the market. It is specifically designed to keep the wind from cutting into the bag while you sleep. The company brags about how the filling is tested twice before the bag is released for sale, and the bags are at least partially constructed in America.

Using the face muff without Velcro prevents your face from being scratched while you sleep, and since the bag is meant to be used in moderate weather, the face muff should function to keep out what chill that the lack of a draft collar would normally let in. The face muff is positioned so that the zipper and the hood draw cord will be away from your face while you sleep.

Zipper guards and draft protection keep the normal dangers of sleeping next to a zipper away from your flesh. Ground level side seams mean that the top of the bag functions more like a blanket, draping over your body instead of dragging the bottom half up to meet halfway like most bags do.

Warmth/Temperature Rating

The Marmot Atom sleeping bag system is designed to be used in moderate, dry weather only. Like with any goose fill down bag, the stuffing needs to be kept dry in order to keep you warm. The water resistant outer shell will repel a normal night's dew fall or condensation while inside a tent, but isn't designed to keep you dry if it gets wet.

Temperature rating for this system has a very small window of reported comfort, resulting in the lower score. Many cold sleepers report that around 40F they will start feeling cold in the bag, while others say that above 50F, the bag is too warm and needs extra ventilation.

The cold sleeper will need to keep this bag in warmer conditions, or paired with thermal mat underneath. This bag is designed for three season use during late spring, summer, or early fall only. Once the temperature begins to drop, a different bag is recommended.


The baffles are sewn through in many spots, helping to keep the baffling where it belongs throughout the bag. This results in less baffling needed, which reduces the overall weight of the bag.

At less than two pounds, even for the long version, the bag's weight makes it ideal for the backpacker. It is hardly noticeable in a pack. The included stuff sack will reduce the bag size to a mere 6 x 6 inches, making the bag take little room in the pack as well as adding little weight. Many users comment on how unbelievably light the bag's construction is.


The bag has been seen for prices ranging from $200 to $309, making it affordable for almost anyone. Hidden costs don't seem to be an issue with this bag. Many users agree that the bag's offerings make it well worth the price.

Common Complaints / Problems

Many users report that the bag has a bad habit of feather poke-through on the inside polyester. Feathers need to be pushed back through upon occasion, and may result in the occasional poke in your sleep.

The bag has had some issues with cold spots reported when the temperature begins to drop, but pairing the bag with a thermal mat seems to solve this situation. The bag's small comfort zone means that you need to be very aware of the expected temperatures before you go camping, so that you can plan accordingly. Below 40F, using a bag liner seems to keep sleepers warm down to about 25F.

Summary - Overall

The Marmot Atom mummy style bag is ideal for moderate weather camping conditions. It is perfect for the backpacker, due to its lightweight design and compression abilities.

It will also fit well into the car camping style, but can't be trusted to weigh the tent in place in the wind.

The couple of issues with the down feathers leaking and cold spots are inevitable with an 850 fill down bag and other factors which we would definitely overlook based on the many advantages the Marmot Atom offers.

Minimum Temperature: 40F / 4C
Insulation: 850+ goose down.
Weight: Regular 1.5 lbs. Long 1.8 lbs.
Shell: Nylon
Max Lenth:Regular 6'0" 72 inches, Long 6'6" 78 inches.
Girth: Regular (shoulder 62" - Hip 58") Long (shoulder 64" - Hip 60")
Stuff Sack: Yes
Hooded: Yes
  • With its 850 goose down fill, this mummy style bag's nylon ripstop exterior is water resistant, keeping the stuffing dry during standard dew or condensation situations. The interior lining is a soft polyester, made of 100% recycled ripstop material.

  • The baffles have been sewn through, keeping the filling in place and making the weight lighter. Complete with a zipper draft tube, face muff, and a six chamber baffled hood, this unit is designed to keep the camper warm in moderate conditions.

  • The regular style weighs a mere 1 pound, 5 ounces. It will sleep someone who stands up to 6 feet tall. The shoulders offer 62 inches of room, with 58 inches offered at the hips, and a roomy foot box of 40 inches.

  • The long style weighs 1 pound, 8 ounces. It will fit someone up to 6 feet, 6 inches tall. Shoulder room is given at 64 inches, with 60 inches around the hips. The foot box has 42 inches of space to kick around in.

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