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NEMO Sonic 0 Down Sleeping Bag Review

The NEMO Sonic 0 Down Sleeping Bag has Thermo-Gills that let you vent the warmth of the bag up to 20 degrees without introducing drafts, so you can use it in warmer temperatures.
The NEMO Sonic 0 Down Sleeping Bag has Thermo-Gills that let you vent the warmth of the bag up to 20 degrees without introducing drafts.

NEMO Sonic 0 Down Sleeping Bag

Warmth
Weight
Comfort
Features
Versatility

Excellent

The NEMO Sonic 0 degree down sleeping bag is a spacious cold weather sleeping bag that can be comfortably used by back or side sleepers. Tricked out with top of the line features such as a taped zipper, zipper draft tubes, and large draft collar, the Sonic 0 has innovative Thermo-Gills that let you adjust the warmth of the bag without cracking open the zipper and introducing cold drafts.

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The NEMO Sonic 0 is a 850 down fill power winter sleeping bag that is cut wide around the knees and torso making it comfortable for back or side sleepers, much like NEMO’s spoon-shaped three-season sleeping bags (like the Nocturne 30.) The Sonic 0 also features zippered vents down the front, called Thermo-Gills that allow you to vent the warmth of the sleeping bag up to 20 degrees without having to unzip the bag and introduce drafts. More on these below.

Zipper

Like all good winter sleeping bags, the NEMO Sonic 0 has down baffles that run above and below the zipper to help seal out drafts when you zip it closed. The fabric that runs along the two-way zipper is taped with a fabric cover, a winter sleeping bag essential, preventing zipper snags or tears to the bag’s interior liner. Unfortunately, the Sonic 0 is only available with a left side zipper – I prefer having an option, and a right hand zipper, myself.

The Sonic 0 has a beefy draft collar that runs over the chest and behind your back to prevent the bellows effect when you move around at night.
The Sonic 0 has a beefy draft collar that runs over the chest and behind your back to prevent the bellows effect when you move around at night. The zipper is taped to prevent snags and bordered by down filled draft tubes to seal out leaks.

Draft Collar

The Sonic has beefy draft collar, a down baffle that lays across the top of your chest/neck and loops around your back to prevent the warm air surrounding your feet, legs, and torso from escaping when you move around at night; the so-called bellows effect. The tension and sizing of the draft collar is controlled by an elastic cord/large cord lock (independent of the hood), so you can adjust it while wearing thin gloves. The draft collar is closed inside the bag with velcro, also easy to use when wearing thin gloves (with a little practice.)

Hood

The mummy hood is well-insulated on top of your head and along the sides, but the front hood opening is shaped so you can lie on your side and not exhale into the hood. If there’s one thing I hate about winter mummy bags, it’s waking up in the morning with frost on the inside or sides of my sleeping bag hood. That’s not a problem with the Sonic 0 in my experience, though.

Dimensions

The interior space inside the Sonic 0 will delight people who prefer a wide sleeping bag with lots of space to wiggle around in at night. The dimensions of the 72″, size regular bag I tested are:

  • Shoulder girth: 61″ / 155 cm
  • Hip girth: 58″ / 145 cm
  • Knee girth: 53″ / 135 cm

Horizontally oriented baffles below the chest and over the knees along with stretch construction let you move around freely. There’s also plenty of room inside the Sonic 0 for storing boot liners, electronics, water bottles, and your stuffed animal so they won’t freeze at night, an important consideration when choosing a cold weather sleeping bag.

The Sonic 0 footbox is covered with NEMO's proprietary waterproof/breathable fabric.
The Sonic 0 footbox is covered with NEMO’s proprietary waterproof/breathable fabric.

Exterior Fabric

The exterior shell of the Sonic 0 is covered with a 20 denier nylon ripstop with a very good DWR that beads internal tent condensation on the surface of the bag and prevents it from wetting the down fill. The footbox is covered with NEMO’s proprietary waterproof/breathable fabric called OSMO, which is the same fabric they use on their waterproof/breathable bivy tents like the NEMO GoGo Elite. This is a nice feature for winter camping where you are more likely to experience internal condensation transfer between a tent and your sleeping bag, but it’s largely irrelevant if your most of your trips are just 1 night in length.

Thermo-Gills

The Sonic 0 sleeping bag has two zippers above the chest that you can open to shed heat, raising the temperature rating of the sleeping bag to 20 degrees fahrenheit. This is useful if the temperature is warmer than 0 degrees or you want to make the bag warmer during the night, which is common as your metabolism slows and your body cools down during a long winter night.

The Sonic 0 Thermo-Gills act like cooling fins when unzipped, allowing cold air to reduce the temperature of the warm air trapped by the chest baffles.
The Sonic 0 Thermo-Gills act like cooling fins when unzipped, allowing cold air to reduce the temperature of the warm air trapped by the chest baffles.

The Thermo-Gills are not holes in the surface of the sleeping bag, as you might expect, but act more like cooling fins, allowing cold air to access the interior of the bag’s chest baffles and reduce the temperature of the air that they trap. They have a very noticeable effect on your warmth level when open or closed, but their biggest benefit is that they give you a way to shed unwanted heat without having to unzip the main zipper and introduce cold drafts.

Comparable 0 Degree Down Sleeping Bags

Make / ModelWeightFill PowerDraft CollarPrice
Big Agnes Blackburn UL 02 lbs 12 oz850Yes$500
Big Agnes Orno 02 lbs 7 oz850Yes$560
Feathered Friends Ibis EX3 lbs 1 oz900Yes$635
Feathered Friends Murre EX Women's2 lbs 13 oz900Yes$585
Feathered Friends Snowbunting EX 02 lbs 13 oz900Yes$599
Marmot Lithium2 lbs 9.5 oz800Yes$499
Marmot Never Summer 03 lbs 3 oz650Yes$279
Marmot Ouray 0 Womens3 lbs 10 oz650Yes$309
NEMO Sonic 02 lbs 11 oz850Yes$479
REI Downtime 03 lbs 14 oz650Yes$249
Sierra Designs UL Nitro 02 lbs 8 oz800Yes$379
Sierra Designs UL Nitro 0 Women's2 lbs 7 oz800Yes$379
The North Face Inferno 02 lbs 14 oz800Yes$519
Western Mountaineering Kodiak MF 02 lbs 12 oz850Yes$675

Recommendation

The NEMO Sonic 0 degree down sleeping bag is a spacious cold weather sleeping bag that can be comfortably used by back or side sleepers. Tricked out with top of the line features such as a taped zipper, zipper draft tubes, and large draft collar, the Sonic 0 has innovative Thermo-Gills that let you adjust the warmth of the bag without cracking open the zipper and introducing cold drafts. In addition to winter camping, the Sonic 0 is ideal for early spring, and early winter camping, when it can be difficult to find a sleeping bag that spans three-season and winter temperature requirements.

Likes

  • Thermo-Gills allow you to vent excess heat without drafts
  • Comfortable for back and side sleepers
  • Spacious dimensions for winter gear storage
  • Draft collar and zipper draft tubes
  • Taped zipper prevents snags

Dislikes

  • Left zipper only

Specs

  • Temperature rating: 0 degrees fahrenheit
  • Fill type: 850 Fill Power Down (duck)
  • Fabric:
    • Exterior 20D Nylon Ripstop w/ DWR
    • Footbox OSMO DT W/B w/ DWR
    • Liner: 20D Nylon Mini Ripstop
  • Length: Regular 72″, Long
  • Weight: 2 pounds 11 ounces. (2 pounds 10 ounces on the SH.com scale)
  • Compressed volume: 11 liters
  • See NEMO’s web site for a complete manufacturer specs

Disclosure: NEMO provided SectionHiker.com with a sample sleeping bag for this review.

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5 comments

  1. Great recommendation got my sonic this week in size large. As you point out it is a really well designened bag and I really like the room for pointing my quilt in for additional warmth. Anxious to try it out! Thanx for a great review

  2. Hi Phil, Douchepacker here. I’ve been eyeing this bag and Im wondering if this is a winner that you’ve continued to use?

  3. Review seems pretty much aligned with my experience. It is a good bag and a decent value, with a couple of caveats:
    It has less fill than most other zero bags, and coupled with the higher volume that means it is not as warm and it takes more to keep it warm. Zero would definitely be pushing it without wearing other insulation in it.

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