The Nemo Sonic is one of the most comfortable bags in our review. It has a super wide cut, a little stretch around the foot box, a big hood, and comes loaded with unique features. Our testers could toss and turn throughout the night to their heart's content. We achieved sublime slumber in all positions, whether flat on our backs, prone, or even curled up in a ball. All this comes at a weight and compressibility equal to or greater than many of the other cold-weather down bags in this category. It lost points in the warmth metric for the same reasons it did so well in comfort. There's lots of space to move around in, which equals less insulated space between the sleeper and the freezing cold. But, if you place a premium on comfort, this is the bag we recommend.Editor's Note: This review was updated on September 29, 2022, with information about updates to the Sonic 0 bag.
NEMO Sonic 0 Review
Cons: Significantly less warm than similarly rated bag, enormous footbox, vents
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Our Analysis and Test Results
Nemo updated the Sonic 0 since our last test period. The side-by-side images above show the bag we tested (left) next to the new bag (right). The new bag has an updated profile and a chevron baffle pattern that's intended to keep the down from migrating. The Thermo Gills now feature a multi-stage zipper system, with both internal and external zippers to help regulate temperature better. Additionally, the liner and shell materials are now 100% recycled and bluesign approved.
This contender gets our best comfort nomination because of its versatility and the fact that it gives you the freedom to roam, both in the bag (because of its spaciousness) and out of the bag (due to its low weight and packability). The downside? More space equals less thermal efficiency, and this bag did not feel as warm as similarly rated bags.
The Sonic contains 24oz of high-quality 800 fill power hydrophobic down. While this makes for low weight and great packability, it significantly detracts from the warmth of the bag. This bag isn't as lofty as some other high bags we've used with the same fill power down. The roomy 58 inches of girth at the hips and the stretchy foot box make for a lot of uninsulated space, making it less warm.
A good way to help insulate the dead air space is to stuff a down jacket into the bottom of the bag or let it rest on top of your hips. Our testing team found it hard to call the Sonic a true 0-degree (F) bag when compared to the high-end competition.
The Sonic is a lightweight 2.95 lbs. This is especially impressive considering that it has one of the widest cuts of any of the bags, two long, zippered vents, and draft tubes above and below the full-length zipper.
Additionally, we felt the lightweight 20 denier ripstop shell fabric did a fine job against rocks and sticks, and we appreciated the even tougher 40 denier nylon that reinforces the foot box for when we needed to roll and scoot around in camp to make a morning cup of coffee.
The comfort metric is where the Sonic reigns supreme. The wide cut allowed our testers to sleep comfortably in any position. The 58" of girth around the hips, plus the slight stretch in the foot box, allowed our restless, finicky sleeping testers to move their knees all the way up to their chests inside the bag. You want to sleep with one leg bent and one leg straight like you're doing the can opener off the diving board all night long? No problem with this bag.
While not the warmest bag, the hybrid baffle system - with vertical baffles in the upper two-thirds of the bag and horizontal in the feet - helps to keep your core area warmer and allows for the inclusion of the two vertical zippered vents. Nemo claims that these vents can change the temperature range of the bag upwards as much as 20 degrees. We felt this was difficult to test, but the vents cooled us down a little when they are open, without letting in cold drafts around the feet like when you use the side zipper to cool off in a conventional bag.
The Sonic is impressively compressible. It packs down to 18"x11" in its included compression sack. We appreciate products that come with a compression sack.
The lightweight shell fabric and 24 oz of goose down keep this bag's packed size down despite it being a big, roomy bag. If you want to forgo the stuff sack and just cram it in the bottom of your pack like our lead tester, stuff it in head first with the beefier 40 denier nylon bottom of the bag on top to protect the bag from the rest of your gear.
The Sonic, light and compressible as it is, has loads of features. The hood is roomy and well insulated, featuring a drawstring for the hood and a separate drawstring for the draft collar. The draft collar has a velcro closure system, so you can snugly seal the collar all the way around your neck. When our testers left the draft collar open, a tab flips down to cover the scratchy velcro and protect the sleeper from nighttime scratches.
Just outside the draft collar is a small storage pouch with a tiny zipper. This pouch was difficult to locate in the dark, and we'd prefer an interior pocket so our batteries and electronic devices can stay warmer. The zipper is lined with an upper and lower draft tube. Stiff tape on either side of the zipper closure makes for a smooth and snag-free pull.
Moving down to the middle of the bag, there are two long, zippered Thermogills. They don't open the bag to cold air as when opening the side zipper. Instead, they create a long narrow strip down the bag where there is what feels like no down between the sleeper and the elements, only the shell fabric. When closed, the baffles are pulled back together, eliminating the uninsulated space.
How effective these zippered vents actually are was a big topic of debate among our testers. Nemo says they can extend the range of the bag upwards of 20 degrees. Most of our testers liked the cool spots they create on the top of the bag, while one tester felt that they didn't make any difference. In the sunlight, you can see more light coming through when the vent zippers are open, as there is no down insulating the vents. Nemo incorporates this feature without adding much weight or bulk. The zippers for vents are super small; we hardly notice them when the vents are closed. The horizontal baffles at the foot box contain some elastic that helped to counter the dead air space when our testers slept with their legs together.
The Sonic's DWR-treated shell did an excellent job repelling water. In our light rain test, water beaded up on 20 denier nylon shell fabric and was easily shaken off, and the reinforced foot box absorbed very little water, even in our submersion test. This bag does have a hydrophobic treatment in the down. In our testing and experience, however, we find that a quality shell fabric is more important for maintaining loft and increasing drying time.
The upper and lower draft tubes are not as efficient as the larger, loftier single draft tubes in the other bags. Our testers occasionally noticed the cold, wet zipper when changing positions inside the bag. This problem isn't a huge concern if you are carrying a tent or bivy sack, but it might be considered if you are planning on a lot of open bivies.
Considering the quality, comfort, and features of the Sonic, we feel it is a good value. The zippered vents increase this bag's versatility, which means more comfy nights sleeping under the stars for your buck.
If you are uncomfortable sleeping on your back in a tight mummy bag, consider this contender. Its wider cut allows for various sleeping positions, while high-quality materials make it suitable for lightweight adventures where a good night's sleep is essential for daytime adventures.
— Matt Bento
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