The temperature rating on a sleeping bag is a marketing number. The actual rating you should care about is 5-10°F colder than the worst night you expect. The fill type, the cut, and how it fits your body matter more than the price tag. Here's how to choose.
Temperature rating — the real one
Bags are sold by 'comfort' rating (warmest you'll be comfortable, average sleeper) and 'limit' rating (coldest you can survive without losing sleep, average sleeper). Most listed temperature ratings are the limit rating, which optimistic.
Pick a bag rated 5-10°F colder than the coldest night you expect. If you're going to high alpine country in summer (35°F nights possible), pick a 20°F bag. If you're going winter (5°F nights), pick a 0°F bag.
Fill type — down vs synthetic
Down (650-fill, 800-fill, 900-fill): warmer per ounce, more compressible, lighter, more expensive. The number is fill power; higher is better. 800-fill is the sweet spot for most buyers.
Down's weakness: it loses 60% of its loft when wet. Useless in damp environments unless you're disciplined about keeping it dry.
Synthetic (Climashield, Primaloft): heavier per ounce, less compressible, retains warmth when damp, cheaper. The right choice for coastal trips, winter expeditions, and anywhere you can't guarantee dry conditions.
Hybrid fills
Some bags use down on top (warmth) and synthetic on bottom (where compression negates down's loft). These are excellent for fast-and-light. Heavier than full down, lighter than full synthetic.
Cut — mummy vs rectangular
Mummy: tapered, hooded, less interior space, warmer for the weight. The default for backpacking.
Rectangular: roomy, can unzip flat as a quilt, less efficient. Fine for car camping where comfort beats weight.
Quilts: open-bottomed, paired with a sleeping pad. Save weight, but require more discipline (drafts).
Length and width — fit matters
- Regular: up to 6'0"
- Long: 6'0" to 6'6"
- Extra-long: above 6'6"
A bag that's too long has dead air space at your feet that you have to warm. A bag that's too short means cold feet pressed against the foot box.
Other features that matter
- Hood with drawcord — critical for cold sleeping; pull the hood tight around your face
- Draft collar at the neck — seals warm air in
- Anti-snag zipper
- Two-way zipper — vent feet without opening the whole bag
How to extend your bag's range
- Liner — adds 10°F
- Wear baselayers — adds 5°F
- Use a balaclava — adds 5°F
- Hot water bottle in the bag — adds 5°F for the night
The right sleeping bag is one you don't think about. If you're shivering or sweating, it's the wrong bag.
Sleeping bags we trust: shop the GemGear sleeping systems collection.