RidgeSyncBackpacking Sleeping Bag Guide: Temperature Rating, Fill, and Fit
A sleeping bag is the piece of gear people most often buy wrong, either too warm and heavy for the trips they actually take, or optimistically rated and cold on the first real night out. Getting it right means understanding what the temperature rating on the tag actually promises, choosing the right fill for your climate, and being honest about how cold you personally sleep.
Buy for your coldest realistic night, not your average one, a warm bag on a mild night is a non-issue; a cold bag on a freezing one ruins the trip.
What the temperature rating actually means
Most reputable bags carry an EN or ISO rating with two numbers: a 'comfort' rating (where an average cold sleeper stays comfortable) and a 'lower limit' or 'survival' rating (where an average warm sleeper stays merely alive, not comfortable, shivering to stay warm). Marketing headlines usually quote the lower limit, which is why a '20 degree bag' can feel cold at 30.
Rules of thumb: buy for the comfort rating, not the lower limit, and if you sleep cold, subtract another 10 to 15 degrees of buffer from whatever number is on the tag.
Down vs synthetic fill
- Down: best warmth-to-weight ratio and compresses smallest, but loses insulating power when wet and costs more; modern hydrophobic-treated down resists moisture better but isn't waterproof
- Synthetic: keeps insulating (imperfectly) when wet, dries faster, costs less, but is heavier and bulkier for the same warmth and breaks down faster over years of compression
- Fill power (600 to 900+) measures down quality, not warmth directly, higher fill power means the same warmth for less weight, not a warmer bag outright
- Choose synthetic for wet climates, budget builds, or a starter bag; choose down for weight-focused trips in drier conditions where you can protect it from soaking
Quilts vs mummy bags
Mummy bags fully enclose you, including a hood, and are the standard choice for cold-weather warmth and simplicity. Backpacking quilts drop the zipper, hood, and often the underside insulation (since a sleeping pad already insulates from below), saving real weight for people who sleep well without a fully zipped cocoon.
Quilts demand a slightly different sleep style, they attach to your pad and rely on you not tossing free of the edges, so try one before committing for a cold-weather trip.
Fit, shape, and length
A bag that's too roomy wastes body heat warming empty air; too snug compresses insulation and creates cold spots, and restricts side sleepers. Most brands offer regular and long lengths and often women's-specific cuts with more insulation at the feet and hips, try the actual size before buying if you can.
Mummy tapering (narrower at the feet) saves weight and traps heat efficiently but limits sleeping position; rectangular and semi-rectangular bags trade some efficiency for room to move.
Matching the bag to the trip
Most three-season US backpacking is well served by a 20 to 30 degree Fahrenheit bag; add a liner or a lighter bag for summer-only trips to save weight, and step up to a 0 to 15 degree bag for shoulder-season or high-alpine nights. Layer a liner inside any bag to add roughly 5 to 15 degrees of range without buying a second bag outright.
Whatever you choose, protect it: pack it in a dry bag or trash-compactor liner regardless of fill type, a wet sleeping bag is a genuinely dangerous problem on a cold night.
Frequently asked questions
What temperature rating sleeping bag do I need?
Buy for the comfort rating, not the lower-limit number in marketing, and choose the rating for your coldest realistic night on the trip, not the average. Most three-season US backpacking is well covered by a 20 to 30 degree bag.
Is down or synthetic fill better for backpacking?
Down offers the best warmth-to-weight ratio and packs smaller, ideal for weight-focused trips in drier climates. Synthetic keeps insulating when wet and costs less, making it the safer choice for humid or wet-prone trips.
What is a backpacking quilt?
A quilt drops the zipper, hood, and often underside insulation of a mummy bag to save weight, relying on your sleeping pad for warmth from below. It suits people who sleep well without a fully enclosed bag.
Can a sleeping bag liner make my bag warmer?
Yes, a liner typically adds roughly 5 to 15 degrees of warmth range and keeps the bag cleaner, a cheap way to extend one bag's usable season instead of buying a second.