The Nemo Sonic is the most comfortable bag 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 at a weight and compressibility equal or greater than most of the other cold-weather down bags in this category. The Nemo Sonic receives our Top Pick for Comfort. 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. Additionally, this bag has less down than eight of the other bags. For a much warmer bag that's nearly as comfortable, check out the Western Mountaineering Kodiak MF.
NEMO Sonic 0 Review
Compare prices at 2 resellers Pros: Comfortable, spacious, lightweight
Cons: Not as warm as similarly rated bags, zipper snags on draft tubes
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Our Analysis and Test Results
This contender gets our Top Pick for Comfort Award 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 light weight and packability). The downside? More space equals less thermal efficiency, and this bag did not feel as warm as similarly rated bags such as the Western Mountaineering Versalite.
The Sonic contains 23.6oz of high quality 850 power 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 the heavier Rab Ascent 900 or the lightweight Western Mountaineering Versalite (which curiously, has a claimed fill weight of 20 oz, but has more loft than many of the other bags). The roomy 58 inches of girth at the hips and the stretchy foot box makes for a lot of uninsulated space, making this bag much less warm than the snug-fitting Feathered Friends Snowbunting.
A good way a 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 bag when compared to the Snowbunting or the Rab Ascent, and a few found the lighter Western Mountaineering Versalite felt warmer.
The Sonic is a lightweight 2 lb 10.2 oz, a hair lighter than the manufacturer's claimed weight. This is especially impressive considering that it has the widest cut 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 an essential 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 in 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 definitely 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 was only out-compressed by the Western Mountaineering Versalite. It packs down to 18"x11" in its included stuff sack, but we crammed it down smaller with our compression sack.
The lightweight shell fabric and 23.6 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 foot on top to protect the bag from the rest of your gear.
The Sonic, light and compressible as it is, has loads of features. Starting from the top, 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, the unfastened velcro stayed out of the way and never scratched their faces in the night.
Just outside from 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 if the pouch was on the inside so our batteries and electronic devices can stay warmer. The zipper is lined with an upper and lower draft tube. These tended to snag in the zipper and didn't keep out the cold as well as the single overstuffed draft tube design in the Western Mountaineering bags.
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. Some of our testers like the cool spots they create on the top of the bag, while one tester felt that they didn't make any difference. What is cool is that 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 doesn't have a hydrophobic treatment in the down, but we found in our testing that quality shell fabric is more important for maintaining loft and increasing drying time. The one weak point in this bag concerning weather resistance is the double draft tube.
The upper and lower draft tubes are not as efficient as the larger loftier single draft tubes in the other bags, and 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 should be considered if you are planning on a lot of open bivies.
The lightweight and compressibility of this bag make it an excellent choice for backpacking, especially if you are a finicky side sleeper or a larger person that finds narrower bags uncomfortable. If you need a bag that is warmer but still lightweight, check out the Western Mountaineering Kodiak MF, the Western Mountaineering Antelope MF, or the Feathered Friends Snowbunting.
We believe $480 is a good value considering the quality, comfort, and features of the Sonic. The zippered vents increase the versatility of this bag, 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