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- Lowest Headline Rating of These TwoNEMO Sonic -20Check price on Amazon
- Only One With Full Rating Details ListedMountain Hardwear Phantom 0Check price on Amazon
The Short Answer: the two bags answer different questions, so pick on what the pages list. The NEMO Sonic -20 has the lower headline rating, -20 F, with vents and a waterproof footbox, but it is the heavier and bulkier of the two by listed figures. The Mountain Hardwear Phantom 0 lists 0 F and gives all three EN numbers, with a comfort rating of 12 F, not 0 F. The two ratings are not shown on one shared basis.
We compared the makers’ published specs; we did not use these bags ourselves. Every figure below comes from the maker pages and from ISO’s summary of the standard, for the NEMO Sonic and the Mountain Hardwear Phantom 0. Our affiliate disclosure explains how links work.
How we picked
A cold weather bag comes down to its rating, its fill, what it weighs and how big it packs. We kept two down bags with a listed rating of 0 F or lower from makers that publish a full spec sheet. We use the makers’ words and numbers only, and we do not rank products on a figure that a page leaves out.
Quick comparison
Figures are as each maker lists them. NEMO lists a minimum weight and a packed weight for the Regular. Mountain Hardwear lists one approximate weight for the bag alone, and says it leaves out both sacks. The two weights are therefore not measured the same way, and the table shows what each page gives.
| Bag | Listed rating | Rating details on the page | Fill | Weight as listed | Packed or stuff size, as listed |
|---|---|---|---|---|---|
| NEMO Sonic -20 (Regular) | -20 F | ISO rows blank for the -20 F Regular | 800 FP down; 2 lb 5 oz (1.06 kg) | 3 lb 14 oz (1.76 kg) minimum; 4 lb 1 oz (1.9 kg) packed | 14.5 x 10.5 in diameter; 12.5 L compressed |
| Mountain Hardwear Phantom 0 | 0 F (-18 C) | EN: comfort 12 F, limit 0 F, extreme -36 F | 800-fill goose down; 805 to 925 g by size | About 2 lb 10.4 oz (1201 g), bag only, size not given | 16.5 x 8.25 in stuff size; 9.7 L compressed (Regular) |
What the ratings tell you
A temperature rating only means something if you know how it was set. ISO says its standard for sleeping bags, ISO 23537-1:2022, sets requirements, test methods and labelling for adult bags with a limit temperature of -20 C or higher. The Phantom page does not name ISO 23537. It lists EN ratings and gives all three numbers: a comfort rating of 12 F, a limit of 0 F and an extreme of -36 F. Its 0 F headline matches its EN limit figure.
The Sonic page is less clear for the bag in this guide. NEMO shows ISO Comfort and ISO Limit rows for the -20 F Regular, but they have no values on the page we read. The same page lists the Sonic 0 F Short with an ISO Comfort rating of 14 F (-10 C) and an ISO Limit of 0 F (-18 C), which is a different bag.
That means the -20 F and 0 F headlines are not directly comparable. We can say the Sonic has the lower headline number. The Phantom page also lists an EN extreme rating of -36 F, a different measure from the limit. NEMO says the Sonic is built to be the only bag you need from -20 F to 40 F, and sells it as -20 F and 0 F options in several lengths. Look at the maker page for the rating details before you rely on a number.
Weight, fill and packed size
The Sonic -20 Regular holds 1.06 kg of 800 FP down, and the Phantom Regular lists 865 g of 800-fill down.
On weight, the Sonic lists 1.76 kg as its minimum and 1.9 kg packed. The Phantom lists about 1201 g for the bag only, with no weight for each size and with both sacks left out. So the Sonic is heavier by the listed figures, but the Phantom’s listed weight leaves out both sacks.
Packed size follows the same pattern. NEMO lists 12.5 L compressed for the Regular. Mountain Hardwear lists 8.9 L Short, 9.7 L Regular and 10.5 L Long. If pack space is tight, the Phantom Regular is the smaller of the two on those figures.
The Sonic is heavier by the listed figures, but the Phantom’s weight leaves out both sacks.
Fit and size
NEMO lists the Sonic -20 F in Regular and Long. The Regular fits up to 6 ft (183 cm), with shoulder, hip and knee girths of 63, 58 and 53 in. Mountain Hardwear lists the Phantom in Short, Regular and Long, with maximum user heights of 68 in (173 cm), 72 in (183 cm) and 78 in (198 cm). The Phantom Regular lists a shoulder circumference of 58 in (147 cm), a hip circumference of 52 in (132 cm) and a footbox circumference of 43 in (110 cm).
The Sonic lists 5 in more at the shoulders and 6 in more at the hips than the Phantom Regular. Mountain Hardwear describes the Phantom as a performance mummy that is wider at the shoulders and hips and tapers toward the legs and footbox, so a buyer who wants room to move should check the girths against their own build. We cannot compare the Sonic knee girth with the Phantom footbox, since they measure different places.
Our picks
Both bags are down bags with listed ratings of 0 F or lower. The two picks follow, each judged only against the other on what its page shows.
The lower headline rating of the two, with vents, a waterproof footbox and more down by weight, at the higher listed weight. Who it's for: A cold-weather backpacker who puts the lowest headline rating and adjustable venting first and will carry extra weight and bulk. A 0 F down bag that lists comfort, limit and extreme EN ratings, with a down-filled face gasket and left- or right-hand zippers. Who it's for: A buyer who wants the rating details on the page, including the comfort figure, and a smaller packed bag.
NEMO Sonic -20
Strengths
Drawbacks
Mountain Hardwear Phantom 0
Strengths
Drawbacks
Zippers, hoods and drafts
The Sonic lists a left-side zipper and an offset zipper. NEMO also lists a redesigned draft collar and bolstered draft tubes, plus chevron baffles and stretch panels at the knees. The shell is 20D recycled nylon ripstop with DWR, and the lining is 20D recycled polyester taffeta with DWR. NEMO says the shell and liner fabrics are 100% recycled and bluesign approved.
The Phantom lists a two-way #5 zipper, offered in left-hand and right-hand versions for zip-together use. It has a four-chamber hood with an external cinch, a draft collar and a down-filled face gasket. Mountain Hardwear says angled horizontal baffles near the hood limit down migration, and that the black lining retains warmth and dries quickly. The shell is a 10 denier recycled fabric with a 15D nylon ripstop lining.
How to choose
- Read the rating basis. Only the Phantom page gives EN numbers for the bag compared here. If you plan around a comfort rating, that is the page that lists it.
- Check the length. The Sonic -20 Regular fits up to 6 ft, and NEMO also lists a Long. The Phantom lists Short, Regular and Long, with heights up to 78 in.
- Compare weight on one basis. The Sonic lists a minimum and a packed weight, and the Phantom lists one approximate weight without sacks.
- Look at the extras you will use. The Sonic lists vents and a waterproof footbox. The Phantom lists a face gasket and a four-chamber hood.
- Check the product page. Make sure it shows the rating and length you want before you buy.
A bag works with the rest of your sleep system. See our camping and backpacking guides, or browse all of our buying guides.
Bottom Line
Choose the NEMO Sonic -20 if the lower headline rating and the vents matter more than weight and bulk. Choose the Mountain Hardwear Phantom 0 if you want EN comfort, limit and extreme numbers on the page and a smaller compressed size. Either way, a 12 F comfort rating or a blank ISO row is worth knowing before a cold night.
Frequently asked questions
Which of these bags has the lower rating?
The NEMO Sonic -20 has the lower headline rating, -20 F, and the Phantom 0 lists 0 F. The bases differ: the Phantom page gives EN ratings, including an extreme of -36 F, and the Sonic -20 Regular ISO rows are blank on the page we read.
What is the Phantom 0 comfort rating?
Mountain Hardwear lists a T-comfort of 12 F (-11 C), a T-limit of 0 F (-18 C) and a T-extreme of -36 F (-38 C).
Which bag has more down?
The Sonic -20 Regular lists 1.06 kg of 800 FP down. The Phantom Regular lists 865 g of 800-fill goose down.
Which is lighter?
The Phantom, by the listed figures: about 1201 g for the bag only, against a 1.76 kg minimum for the Sonic. The Phantom weight leaves out its sacks and gives no size.
Which packs smaller?
The Phantom Regular lists 9.7 L compressed and the Sonic -20 Regular lists 12.5 L.
Does a rating mean the same thing across makers?
Not necessarily. ISO says its standard sets requirements, test methods and labelling for sleeping bags, but the Phantom page does not name ISO 23537, the Sonic -20 Regular ISO rows are blank, and only the Phantom lists EN ratings.