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NEMO Sonic 0 Sleeping Bag Review

NEMO Sonic 0 Sleeping Bag Review

The NEMO Sonic 0 is a down-insulated sleeping bag that can be comfortably used from zero degrees Fahrenheit up to 40 degrees. (This is the 2022 version which has been significantly updated from previous models.) While the Sonic 0 can be used as a winter sleeping bag and has all the advanced features you’d expect, it has special thermo-regulation gills on the chest that let you vent it in warmer weather. If you’re a cold sleeper or want a single sleeping bag that can span winter-to-spring or fall-to-winter temperatures, I think you’ll be impressed by the NEMO Sonic 0’s versatility and comfort.

Specs at a Glance

  • Gender: Unisex
  • Tested Lower Limit: 0F
  • Tested Comfort Limit: 14F
  • Insulation: 800 fill power
  • Water-Resistant Down: Yes
  • Weight: 3 lbs 4 oz (3 lbs 6.7 oz actual)
  • Down Fill Weight: 28 oz
  • Length: 72 inches tested (66″, 78″ also available)
  • Girth: Shoulder (63″), Hip (58″)
  • Compression Sack Weight: 3.4 oz (included)
  • Storage Bag: Included

Sleeping Bag Features

The Sonic 0 has all of the standard features you’d expect on a premium cold weather sleeping bag, including a draft collar, two-way side zipper, zipper draft tubes, taped zipper stiffeners, spacious dimensions, and a very warm hood. It also includes two fairly unique features, which differentiate it from most other cold weather sleeping bags: Therm-Gills and Waterproof Ends (footbox and hood).

Draft Collar

 that wraps over your upper chest and back. It closes with velcro tabs and can be tensioned with a cord lock inside the bag when the bag is zippered closed
The draft collar wraps over your upper chest and back. It closes with velcro tabs and can be tensioned with a cord lock inside the bag when the bag is zippered closed.

The draft collar is a down-filled tube that drapes over your upper chest and neck and around your upper back to seal in the heat generated by your lower body. It is secured on one side by velcro and tensioned on the other side with an elastic cord and cord lock that is easy to use with one hand when the bag is closed and zippered up.

Two-Way Zipper and Draft Tubes

There’s a 3/4 length two-way zipper that begins above the footbox and runs all the way to the hood. Having a two-way zipper lets you vent the bottom of the bag if you’re too warm. The zipper has two draft tubes (most bags only have one) that run alongside the zipper and fold together to block any drafts from entering through it. The fabric along both sides of the zipper also has a fabric stiffener to prevent the slider from snagging and tearing on the bag’s fabric which is very helpful on a high fill bag.

It’s a little hard to see here, but there is a fabric stiffener on both sized of the zipper to prevent snags
It’s a little hard to see here, but there is a fabric stiffener on both sides of the zipper to prevent snags.

Wide Girth

Dimensionally, the Sonic 0 is cut wide so you can store extra gear, your boots, or water inside with you when you sleep to prevent them from freezing. That extra width also lets you sleep on your side or move around at night with ease. If you have to 12 hours in a sleeping bag, you’ll appreciate the extra room!

Mummy Hood

The Sonic’s hood is shaped more like the hood of a jacket than a traditional mummy hood.
The Sonic’s hood is shaped more like the hood of a jacket than a traditional mummy hood.

While the Sonic 0 has a mummy hood, it’s shaped more like a jacket hood with close-fitting sides than a more conventional arched bag-width mummy hood. The fitted sides mean that the hood moves with your face when you turn, giving you the ability to sleep on your side in the bag, without drenching the side of the hood with moist exhalations. NEMO’s spoon-shaped sleeping bags transformed sleeping bag design by making it possible for side sleepers to get a good night’s sleep so this feature is consistent with their core DNA.

NEMO Sonic 0 Sleeping Bag


Optimized Thermal Design

The Sonic 0 has Thermogills, which let you adjust the amount of warmth retained by the sleeping bag. These allow the Sonic to be used from 0 up to 40 degrees. That's a remarkable feat of product design.

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But there are more differentiating features on the Sonic 0 that you just won’t find on other comparable sleeping bags, including the Thermo-Gills and a waterproof footbox and hood.

When unzipped the Thermo-Gills release some of the warm air trapped in the chest baffles
When unzipped the Thermo-Gills release some of the warm air trapped in the chest baffles and help keep you cooler.


Thermo-Gills are lengthwise zippered channels sewn over the chest of the Sonic 0 that release some of the warm air trapped in the down baffles without letting drafts in. Earlier versions of the Sonic had these zippered channels on the outside of the bag only, which made them impossible to reach if you were snuggled inside. While they were still useful, the new version of the Sonic adds another pair of zippers on the inside of the bag so you can further adjust your warmth level without getting chilled.

For example, if you run your hand down the front of the chest (on the inside) when the outer or inner zippers are opened, you can feel that the liner is noticeably cooler than on either side. If you’re still too warm, you can loosen the draft collar and let additional heat out. I’ve taken the Sonic 0 up to the mid-forties (F) using these temperature regulation features and have been really impressed by how well they work.

If you’ve ever slept in a single wall tent, it’s common to wake up with a damp footbox
If you’ve ever slept in a single wall tent, it’s common to wake up with a footbox damp from tent condensation. That was the case when I woke up in this single-wall pyramid tent.

Waterproof Foot Box and Hood

If you’ve ever slept in a single wall tent, it’s common to wake up with a sleeping bag footbox or a hood that’s damp from tent condensation where they touch the walls. It’s also a common occurrence in winter tents, especially when you have to keep the door closed at night. But NEMO has encased the Sonic footbox and most of the hood in waterproof/breathable fabric to prevent the moisture from making the sleeping bag’s down insulation wet.

The portion of the hood where it can touch a tent wall is covered in waterproof:breathable fabric
The portion of the hood where it can touch a tent wall is covered in waterproof/breathable fabric.

For instance, I’ve slept with the Sonic 0 in three different single wall tents and noticed water droplets on the outside of the footbox every time. While the exterior fabric is easily dried by putting it out in the sun while you make breakfast, it’s nice to know that the down insulation, which would take longer to dry, hasn’t gotten wet and will retain its loft, especially on a multi-day trip. It’s the same with the hood, which is also prone to condensation transfer.

Comparison table: 0-degree sleeping bags

Make / ModelFill PowerWeightDown Fill Weight
Marmot Lithium 08003 lbs 0.9 oz33.9 oz
The North Face Inferno 08002 lbs 14 oz29.3 oz
NEMO Sonic 08003 lbs 4 oz28 oz
Therm-a-Rest Parsec 08002 lbs 6 oz26 oz
Western Mountaineering Kodiak 08502 lbs 12 oz30 oz
Feathered Friends Snowbunting EX 09002 lbs 13 oz25.3 oz
Mountain Hardwear Phantom 08502 lbs 10.630 oz
Thermarest Polar Ranger -208003 lbs 4 oz34 oz
Western Mountaineering Puma MF -258503 lbs 7 oz36 oz
Feathered Friends Snow Goose EX -409004 lbs 2.9 oz42 oz


The NEMO Sonic 0 is a cold-weather down-insulated sleeping bag that has a much wider temperature range than its name would suggest. While it is designed to keep you warm in 0-degree weather, it has a temperature regulation feature called Therm-Gills that let you vent warmth up to about 40 degrees. I can’t think of any other cold-weather sleeping bag with that kind of versatility. If you like to winter camp but want to extend the season into early spring or autumn, the Sonic 0 is an excellent option. You can then buy a much less expensive 40+ degree bag or quilt to cover the warmer months.

Now, the ratings for this bag are based on the ISO sleeping bag temperature rating standard, so that 0-40 degree Fahrenheit temperature rating is good for men and warm sleepers. If you are a cold sleeper or a woman, the temperature range will fall between 14 and 40. The difference is due to the fact that women aren’t generally as large as men and don’t generate as much body heat. If you are a woman and need a 0-degree bag, I’d consider the NEMO Sonic -20, which has the same feature set but is rated for colder weather.

Disclosure: NEMO donated a sleeping bag for review.

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  1. Perfect for thru hikers not sure when winter ends and spring begins!

  2. This looks like an awesome bag, though I can’t justify the price at $600. I don’t mind paying a little more for quality but at those prices you’re excluding a lot of would-be interested hikers. Even with a 20% off coupon it’s too much. I’d love to see a side by side comparison of this bag to one half as much. I might actually consider buying it if it achieves a much greater advantage in a comparison. Thanks for this informative review … I can always dream.

  3. I have used this bag on multiple occasions and it has excelled in every way. what hasn’t been discussed is how capably it handles temperature change as related to elevation. This bag handled the higher temperatures associated with the lower elevation approach as well as the sub zero temperatures on the ridges. The water resistant footbox works well. This bag helps me feel safe regardless of what conditions I encounter.

  4. I bought the minus —20*F version because I cowboy camp in the winter. Minus 9*F Is my personal comfort limit for winter cowboy camping while sleeping in one thin base layer, sleep sox and a generic beanie. I’m a bit chunky so a micro puffy or 200 wt fleece is the max I can fit and still be comfortable; of course in a tent with another person I could go so much colder that I’d probably reschedule the outing.
    But get this!
    I’ve cowboyed under this bag “quilt style” at 45*F with the thermogills open, no hat, & my head in the open air and been perfectly comfortable and didn’t break a sweat.
    I have two top of the line bags and both of them cause “cold but syndrome” when I sleep on my side.
    Nemo is definitely right in thinking that side sleepers need different bags. Might be part of why so many women seem to sleep cold… the bottom of many sleeping bags are underfilled & the manikin lab tests do not test side sleeping. These “top bags”lead to cold butt, cold kidneys cold spine when you side sleep. This shunts blood flow to the core & you feel much colder & more miserable than you actually are.
    I have three times added bottom down to a high end super expensive bag and voilà suddenly the rated temp applies to all positions not just back sleeping.

  5. thanks for the review Philip!

    I noticed you mentioned the head and foot box have a waterproof exterior fabric. I’ve emailed Nemo to try and figure out what that fabric is / confirm the details, but all they replied with was that it has a dwr coating. Do you have any more info on the water proof fabric? I was curious if you sprayed water directly on the fabric at all in testing and found nothing got through.

    • I’m just passing along what their product people told me. I suspect that their support person doesn’t know the answer (I could be wrong) because they had different fabric on both ends in the previous 2 versions of this bag I tested as well!

  6. Looking at this bag for my wife- 5’2″. Would it be best to get the short bag for her (66″) or the regular listed as length 72″?

  7. For the occasional winter AMC hut overnights in the Whites or tent camping in moderately cold ( above zero degree forecasted lows) would you recommend this or the WM Kodiak 0?

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