Every recommendation here follows the Trail Gear Journal research and evaluation process.
Cold-Weather Sleeping Bags Compared
| Model | Insulation & shape | Rated to | EN/ISO comfort / limit | Weight (reg) | MSRP* |
|---|---|---|---|---|---|
| REI Co-op Magma 15 | 850-fill down, mummy | 15°F | 21°F / 9°F | ~2 lb 4 oz | ~$399 |
| NEMO Disco 15 | 650-fill hydrophobic down, spoon | 15°F | ~25°F / ~14°F | 2 lb 11 oz | ~$330 |
| Kelty Cosmic Down 20 | 550-fill down, mummy | 20°F | 31°F / 21°F | 2 lb 7 oz | ~$190 |
| Marmot Trestles Elite Eco 20 | Synthetic, mummy | 20°F | ~32°F / ~22°F | ~2 lb 9 oz | ~$190 |
| Big Agnes Lost Dog 15 | Synthetic (FireLine ECO), rectangular | 15°F | Not EN/ISO rated | 3 lb 3 oz | ~$200 |
Manufacturer-published ratings (EN/ISO 23537 comfort/limit where listed). Temperature ratings are planning tools, not guarantees; real warmth depends on your sleeping pad, clothing, and physiology. Weights and prices vary by size and retailer — confirm current pricing on the linked product pages before buying.
The Short Version
If you want the most warmth for the least weight, a high-fill-power down bag like the REI Co-op Magma 15 is the pick; if you camp in damp conditions or want to spend less, a synthetic bag like the Marmot Trestles Elite Eco 20 makes more sense. The number in a sleeping bag's name is usually a lower-limit rating, not the temperature at which an average person sleeps comfortably, so most campers should choose a bag rated a little colder than their expected overnight low. For US campers in the Rockies, Appalachians, desert shoulder seasons, and northern state parks, a 15°F to 20°F bag on a warm pad is a practical cold-weather starting point. The five bags below cover down and synthetic, mummy and rectangular, and budget to premium.
Best Warmth-to-Weight: REI Co-op Magma 15
The Magma 15 is the warmth-to-weight standout here. REI lists it with 850-fill-power water-resistant down, a 15°F rating, EN/ISO comfort and lower-limit figures of roughly 21°F and 9°F, and a regular weight around 2 lb 4 oz, at an MSRP near $399. That combination of high fill power and low weight is why down mummy bags like this dominate the lightweight end of cold-weather camping. It suits backpackers and weight-conscious campers who keep their gear dry; the tradeoff is price and the usual care that down requires around moisture.
Best for Side Sleepers: NEMO Disco 15
NEMO's Disco uses a Classic Spoon shape with extra room at the elbows and knees, which is why owner reviews repeatedly highlight it for side and restless sleepers. NEMO lists 650-fill-power hydrophobic, RDS-certified down, a 15°F rating, and a regular weight around 2 lb 11 oz, with chest Thermo Gill vents for temperature control, at an MSRP in the low-$300s. It is heavier and lower in fill power than the Magma, but the roomier cut and venting make it a comfortable car-camping and shoulder-season down bag for people who do not sleep flat on their back.
Best Value Down Bag: Kelty Cosmic Down 20
The Kelty Cosmic Down 20 is the long-running value pick in down. Kelty lists 550-fill-power down, a 20°F rating with EN comfort and lower-limit figures near 31°F and 21°F, and a regular weight around 2 lb 7 oz, often around $190. The lower fill power means it is bulkier than premium bags, but for campers who want real down warmth without a premium price, it is one of the most recommended budget down bags available and a sensible choice for cold three-season nights.
Best Synthetic Mummy for Damp Cold: Marmot Trestles Elite Eco 20
When conditions are wet, synthetic insulation holds more of its warmth than down, and the Marmot Trestles Elite Eco 20 is a popular synthetic mummy. Marmot lists HL-ElixR Eco synthetic insulation made from recycled, PFC-free materials, a 20°F rating with EN comfort and lower-limit figures near 32°F and 22°F, a second fold-down zipper for ventilation, and a regular weight in the 2 lb 9 oz range, typically near $190. It is the practical choice for humid regions, loaner gear, and campers who do not want to baby a down bag.
Best Rectangular Cold-Weather Bag: Big Agnes Lost Dog 15
Most cold-weather bags are mummy-shaped, so campers who want a roomier rectangular bag have fewer warm options. The Big Agnes Lost Dog 15 is a rectangular system bag with FireLine ECO synthetic insulation (made from recycled materials), a 15°F rating, an integrated Flex Pad Sleeve that locks the bag to your pad, and a regular weight around 3 lb 3 oz, typically near $200. The rectangular cut and pad sleeve trade some thermal efficiency and weight for comfort and the elimination of cold gaps between bag and pad, which is a sensible compromise for car campers who hate feeling restricted.
What About Extreme Cold Below 0°F?
None of the five bags above are extreme-cold or expedition bags. They are rated to 15°F or 20°F, which covers most cold three-season and mild winter camping, not deep-winter or high-altitude conditions. For sustained temperatures below 0°F, look for a bag specifically rated to 0°F, -20°F, or colder, ideally with EN/ISO 23537 comfort figures rather than a single marketing number, plus a full draft collar, an insulated hood, and a pad with a high winter R-value. Stretching a 15°F bag to -20°F with a liner is risky, so treat sub-zero trips as a different category and confirm a true expedition rating before you rely on it.
Lightweight Cold-Weather Options
If packed weight is your priority, fill power does most of the work: higher fill power means more warmth per ounce. Among these picks, the 850-fill REI Magma 15 is the lightest for its warmth at roughly 2 lb 4 oz, followed by the 550-fill Kelty Cosmic Down 20 at about 2 lb 7 oz. Synthetic bags such as the Marmot and the Big Agnes weigh more for the same warmth, which is the expected tradeoff for their moisture resistance and lower price. Backpackers heading into the cold generally favor high-fill-power down kept dry in a waterproof stuff sack.
How to Read a Temperature Rating
A sleeping bag temperature number should be read with caution. Many bags carry EN/ISO 23537 figures: a comfort rating (aimed at a standard cold sleeper) and a lower-limit rating (aimed at a standard warm sleeper). A single marketed number is often close to the lower limit, which a warm sleeper may survive in a curled position rather than enjoy. Women, side sleepers, tired hikers, and people who naturally run cold typically need more insulation. If overnight lows are expected around freezing, plan around the comfort rating, not the headline number.
Down vs Synthetic for Cold Weather
Down insulation wins when packability, long-term loft, and warmth-to-weight are priorities. It costs more and needs care around moisture. Synthetic insulation is bulkier for the same warmth, but it keeps more of its loft when damp and is a smart choice for wet regions, kids, loaner gear, and budget-minded campers. A down bag kept dry in a waterproof stuff sack is excellent for backpacking; a synthetic bag that gets tossed into the back of an SUV by tired campers is a very practical car-camping tool.
Mummy vs Rectangular vs Quilt
Mummy bags are the most thermally efficient because they reduce empty air space and add a hood. Rectangular bags are roomier and friendlier to side sleepers, but they lose heat faster and need more insulation, which is why warm rectangular options like the Lost Dog often add a pad sleeve to cut drafts. Quilts can work well for experienced backpackers chasing low weight, but many car campers prefer the simplicity of a full hooded bag. Match the shape to how you actually sleep and travel, not to a spec sheet.
Don't Forget the Sleeping Pad
A cold-weather bag is only half the sleep system. When the insulation under your body compresses, the pad becomes the thermal barrier, so pad R-value matters as much as the bag's rating in the cold. Look for a pad with an R-value suited to shoulder-season or winter use, and consider layering a foam pad under an inflatable one for extra warmth and puncture backup. If you have ever woken up cold from below while the top of the bag felt fine, the pad was the weak link.
Fit, Hood, and Draft Control
Fit matters because extra space must be warmed by your body. A bag that is too tight compresses insulation and feels restrictive; one that is too roomy feels drafty. Look for a hood that cinches comfortably, a draft collar or tube along the zipper, and a zipper that can vent without opening the whole bag. Side sleepers should check shoulder and knee room. Cold weather punishes small annoyances because you notice every gap at 3 a.m.
Care and Storage
Never store a sleeping bag compressed for long periods. Use the large storage sack or hang it in a dry closet, air it after trips, spot clean when possible, and wash only according to manufacturer instructions. Down bags need careful drying with low heat and patience so the clusters fully re-loft; synthetic bags are more forgiving but still last longer with gentle handling. A bag that keeps its loft is warmer, and loft is the whole game.
Bottom Line
For cold-weather camping, buy a sleep system rather than a number. Match the bag to realistic overnight lows, pair it with a warm pad, keep moisture out, and choose a shape that lets you actually sleep. If you want the lightest warm setup, the REI Magma 15 leads; for value down, the Kelty Cosmic Down 20; for damp cold, the Marmot Trestles Elite Eco 20; for a roomy rectangular bag, the Big Agnes Lost Dog 15; and for side sleepers, the NEMO Disco 15. A slightly heavier setup that gives you eight good hours beats a minimalist setup that looks impressive in a spreadsheet and feels miserable before dawn.
Source Notes
- Temperature ratings vary by standard, brand, and sleeper physiology; this article treats them as planning tools rather than guarantees.
- Pad insulation, dry base layers, and campsite selection can change real warmth more than a small rating difference.
- Specs above reflect manufacturer and retailer listings at the time of writing; confirm current model names, ratings, and pricing on the product pages linked below.
Sources
- REI Co-op Magma 15 Sleeping Bag — Men's (REI)
- NEMO Disco Men's Endless Promise Down Sleeping Bag (NEMO Equipment)
- Kelty Cosmic Down 20 Sleeping Bag — Men's (REI)
- Marmot Trestles Elite Eco 20 Sleeping Bag (Marmot)
- Big Agnes Lost Dog Sleeping Bag Series (Big Agnes)
FAQ
What temperature sleeping bag do I need for winter camping?
For winter camping at or below freezing, plan around a bag rated colder than your expected overnight low, because most ratings describe a lower limit rather than true comfort. A 15°F bag paired with a high R-value pad and dry base layers is a common starting point for cold three-season and mild winter use; deep winter and high-altitude trips usually call for a 0°F or colder bag.
How cold can you use a 15-degree sleeping bag?
A 15°F rating is typically a lower-limit figure, meaning a warm sleeper may get through a night near 15°F but not necessarily comfortably. Many people are most comfortable roughly 10 to 15 degrees above the rated number, so a 15°F bag is often a comfortable choice for nights in the high 20s to low 30s when paired with a warm pad.
Are down or synthetic sleeping bags better for cold weather?
Down offers the best warmth-to-weight and packs smaller, which is why high-fill-power down bags dominate the lightweight end of this list. Synthetic insulation is bulkier and heavier for the same warmth but keeps more of its loft when damp and usually costs less, which makes it a strong pick for wet climates, car camping, and budget setups.
What is the warmest sleeping bag shape?
A mummy shape is the most thermally efficient because it minimizes the dead air space your body must heat. Rectangular bags are roomier and better for side sleepers and restless campers, but they lose heat faster and need more insulation to feel as warm. Some rectangular cold-weather bags compensate with a pad sleeve and a hood to cut drafts.
Is a 20-degree sleeping bag warm enough for freezing weather?
Often, but not always. Many sleepers need a 10 to 15 degree comfort buffer, especially if they sleep cold, use an underinsulated pad, or face wind and damp. At a hard freeze, a 20°F bag is more reliable for warm sleepers in a tent with a good pad than for cold sleepers in marginal conditions.
Does the sleeping pad matter as much as the bag?
Yes. A warm bag on a low-R-value pad can still feel cold because the ground steals heat through the compressed insulation beneath you. In cold weather, pad R-value is just as important as the bag's rating, and many cold nights are fixed by adding pad warmth rather than buying a warmer bag.