Start with the coldest night you expect, choose enough warmth, then check fit and packed size. Before shopping, confirm what your accommodation or guided trip supplies. If camping is only an optional night in an otherwise indoor itinerary, consider renting locally rather than carrying a sleeping bag all week.
1. Choose the temperature rating before the insulation
Use overnight conditions at your actual campsite—not daytime temperatures in the nearest city. Check seasonal lows when planning, then review the forecast before departure. If the route includes several elevations or seasons, identify the coldest overnight stop you intend to keep.
Look for an ISO- or EN-tested rating, and read the specifications rather than the number in the product name:
- Comfort: the useful starting point for cold sleepers or anyone unsure how warm they sleep.
- Lower limit: a colder threshold intended for warm sleepers; it is not interchangeable with comfort.
- Extreme: a survival rating, not a temperature to plan a night’s sleep around.
REI explains the comfort and lower-limit distinction; Sea to Summit advises disregarding the extreme rating.
Choose a rating below your expected low rather than buying exactly to the forecast. Leave more margin if you sleep cold. Ratings assume controlled conditions, including clothing and an insulated pad; real-world warmth varies. An unlabelled brand temperature estimate is less useful for comparisons than a tested comfort rating. REI’s temperature guidance supports choosing below anticipated lows, but no rating guarantees warmth.
If one optional night needs a much warmer, bulkier bag than the rest of the trip, consider changing that overnight stop instead of packing for it all week.
2. Budget for the sleeping pad too
For camping, treat the bag and pad as a pair. A warmer bag does not make an inadequately insulated pad a sound cold-weather setup. R-value measures a pad’s resistance to heat flow; higher values provide more insulation.
Check the pad manufacturer’s guidance for your expected conditions, including for any rental pad supplied by an operator. Bag temperature tests use an insulated pad and base layers, so a thin, poorly insulated pad can undermine the bag’s apparent warmth. REI’s sleep-system guidance explains how the components work together.
3. Pick down or synthetic for your packing constraints
| Choose | When it makes sense | Main trade-off |
|---|---|---|
| Down | You will carry the bag far or have limited luggage space | Usually lighter and more compressible, but more expensive; wet down loses insulating ability |
| Synthetic | Price matters, vehicle space is available, or damp conditions are a concern | Usually bulkier and heavier for similar warmth, but dries faster and insulates better when wet |
These are the principal trade-offs in REI’s insulation comparison. Keep either type dry; synthetic’s moisture tolerance is a fallback, not a reason to accept wet bedding.
Compare bags at the same tested rating and in your required size. For down, fill power describes warmth for the insulation’s weight—not the finished bag’s temperature rating. Check total weight and compressed volume, not just insulation weight. REI’s backpacking guide explains these specifications.
4. Try the fit in your normal sleeping position
A mummy shape saves weight and limits unused space. A semi-rectangular shape offers more movement; rectangular bags prioritize roominess, often at the expense of weight and heat efficiency.
Zip the bag fully and lie on your side if that is how you sleep. Check that you can bend your knees, move your shoulders and relax your feet without pressing hard against the end. Too-tight areas can compress insulation; excessive spare space also makes warmth harder to maintain. Use the manufacturer’s height and girth specifications, not just “regular” or “long.” REI’s fit guidance explains these trade-offs.
5. Check the details that help the trip adapt
Prioritize a usable zipper for ventilation on warmer nights, plus a hood, draft collar and insulated zipper tube for colder ones. Test the zipper from inside the bag.
Pack the bag with your actual luggage before committing. If space is tight, work it into your carry-on packing system for changing climates rather than treating it as an extra strapped on afterward.
Compress it for transport, but store it loosely once home: long-term compression can impair loft and insulation. A liner can help keep it clean and add some warmth, but choose a bag adequate for the trip without relying on a liner to rescue an under-rated purchase. REI covers these features and accessories.