Best sleeping bag for cold weather: read past the name
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Quick answer
A cold-weather bag's name is often far colder than the temperature it keeps you comfortable at. TETON's Celsius XL is called a 0°F bag but lists a comfort rating of 25 to 30°F. Kelty's Cosmic Down 0 lists 5°F on its spec sheet without saying which rating that is. Choose by comfort rating, then build the system: an insulated pad such as Therm-a-Rest's XTherm NXT (R-value 7.3) and, if needed, a liner like Sea to Summit's Reactor Fleeceweight, which adds up to 14°F.
The name is not the comfort rating
Makers name bags by a temperature, but that number is often a limit, not comfort. Three examples from the makers' own pages:
| Bag | Name | Listed rating |
|---|---|---|
| TETON Celsius XL | 0°F | Comfort 25 to 30°F |
| Kelty Cosmic Down 0 | 0 | 5°F (type not stated) |
| Sea to Summit Circuit 15°F | 15°F | 16°F lower limit; 23°F comfort |
The TETON gap is the starkest: a bag sold as 0°F is comfortable to about 25 to 30°F. For a cold night or an outage in an unheated house, pick a bag whose comfort rating matches your coldest expected temperature, and treat lower-limit or unlabeled numbers as colder than you will sleep comfortably.
Two very different cold-weather bags
| Spec | TETON Celsius XL 0°F | Kelty Cosmic Down 0 (Regular) |
|---|---|---|
| Insulation | SuperLoft Elite hollow fiber (synthetic) | 550 fill down, 39.5 oz (1,120 g) |
| Shape | Extra-roomy rectangle with mummy hood, 90 x 36 in | Semi-rectangular, fits to 6 ft |
| Weight | 7.94 lb | 4.34 lb |
| Packed size | 16.75 x 13 x 13.25 in | 10 x 19 in stuff sack |
| Lining | Polyester flannel | Recycled fabric, PFAS-free DWR shell |
| Warmth features | Zipper and shoulder draft tubes, two-way zipper | Full draft collar and draft tube, trapezoidal baffles |
| Warranty | Lifetime | See Kelty |
The TETON is a car-camping and home-emergency bag: roomy, flannel-lined and nearly 8 lb. The Kelty carries a colder listed rating at a bit over half the weight (4.34 vs 7.94 lb) and packs smaller, which matters if you may need to carry it.
Your pad matters as much as the bag
Plan a pad as part of the system. Pads list an R-value; higher means more insulation. Therm-a-Rest's NeoAir XTherm NXT lists:
- R-value 7.3, which Therm-a-Rest calls cold-conquering
- 15.5 oz (440 g) in Regular size, 3 in thick
- 70D nylon on the bottom and 30D on top
- A pump sack, stuff sack and field repair kit included
The same pad works on a cold floor at home during an outage.
Add warmth with a liner
A liner is a thin inner bag that adds warmth and keeps the main bag clean. Sea to Summit lists:
- Reactor Fleeceweight: adds up to 8°C (14°F), with Thermolite hollow-core grid fleece, a fitted hood and arm openings.
- Reactor Midweight: adds up to 6°C (11°F) with Thermolite Pro fabric.
Both are machine washable, and Sea to Summit says using a liner reduces how often you wash the sleeping bag. Treat "up to" figures as best-case additions to a well-matched system, not a reason to under-buy the bag.
Cold-weather sleep checklist
- Match the comfort rating to the coldest night you expect, with margin.
- Use an insulated pad with a high R-value under any bag.
- Close the draft collar and hood on bags that have them; both Kelty and TETON list draft tubes or collars.
- Keep down dry and store bags loose when not in use.
- Never heat a tent with an open flame or fuel heater while sleeping; carbon monoxide builds up in enclosed spaces.
What to look for when you buy
Roomy car-camping example: TETON Celsius XL 0°F
Best for: Home emergency kits and car camping where weight does not matter
TETON lists an extra-roomy 90 x 36 in rectangle with mummy hood, flannel liner, draft tubes, compression sack and a lifetime warranty.
Watch out: Comfort rating is 25 to 30°F despite the 0°F name, and it weighs 7.94 lb.
See options on Amazon (opens Amazon in a new tab)Lighter down example: Kelty Cosmic Down 0
Best for: Cold camping trips where you may carry the bag
Kelty lists 550 fill down (39.5 oz in Regular), a full draft collar, trapezoidal baffles, a 5°F rating and 4.34 lb weight.
Watch out: Kelty does not label the 5°F figure as comfort or lower limit; keep the down dry.
See options on Amazon (opens Amazon in a new tab)Warm pad example: Therm-a-Rest NeoAir XTherm NXT
Best for: Pairing with any cold-weather bag on frozen ground or cold floors
Therm-a-Rest lists an R-value of 7.3 at 15.5 oz for the Regular, 3 in thick, with pump sack and repair kit.
Watch out: Air pads can puncture; carry the included repair kit.
See options on Amazon (opens Amazon in a new tab)Questions people ask
- Is a 0 degree sleeping bag warm enough for 0 degrees?
- Often not. TETON's Celsius XL 0°F lists a comfort rating of 25 to 30°F. Check the comfort rating, not the name.
- Down or synthetic for cold weather?
- Kelty's Cosmic Down 0 weighs 4.34 lb with a 5°F listing; TETON's synthetic Celsius XL weighs 7.94 lb with a 25 to 30°F comfort rating. Keep down dry.
- What R-value sleeping pad do I need for winter?
- Higher is warmer. Therm-a-Rest's XTherm NXT lists 7.3, which it markets for cold conditions.
- How much warmth does a sleeping bag liner add?
- Sea to Summit lists up to 14°F for its Reactor Fleeceweight and up to 11°F for its Reactor Midweight.
Sources
- Celsius XL 0°F sleeping bag: specifications, TETON Sports
- Cosmic Down 0 sleeping bag: specs, Kelty
- Circuit Down sleeping bag: ISO ratings by size, Sea to Summit
- NeoAir XTherm NXT sleeping pad, Therm-a-Rest (Cascade Designs)
- Reactor Fleeceweight sleeping bag liner, Sea to Summit
- Reactor Midweight sleeping bag liner, Sea to Summit