The number on a sleeping bag is the most misread spec in camping. It is usually a survival or limit figure, not a comfort one, and it assumes a sleeping pad, dry clothing and a tent. Read it as a floor, not a promise.
The working rule
Add roughly 10 to 15 degrees Fahrenheit to a bag's rating to get the temperature you will actually sleep well at. A 35 °F bag is a comfortable 45 to 50 °F bag. A 10 °F bag handles a genuinely cold night at freezing. If you sleep cold, add more.
Shape decides warmth as much as fill
- Mummy. Less air to heat, a hood that closes around your head, and the warmest result per ounce of fill. Narrow if you move in your sleep.
- Rectangular. Room to move, zips open into a quilt, and pairs with a second bag. Warm-weather and car-camping shape.
- Oversized or XL. A rectangular bag with 30 percent more room. Comfort first; expect to run cooler than the rating suggests.
Liner material changes the feel more than the number
A cotton flannel lining feels warm immediately and is pleasant against skin, but it is heavier and slower to dry. A synthetic liner is lighter and dries fast, which matters if you are carrying the bag rather than driving it to the site.
The pad is half the system
Most of the heat you lose at night goes into the ground, not the air. A bag rated to 10 °F on bare tent floor performs like a 30 °F bag. If you are buying warmth, buy the pad before you buy a lower rating.
Zip side matters if you pair bags
Two bags only zip together if their zips are opposite-handed. If you are buying a pair, check for a left-zip and a right-zip version — the same model in the same zip does not mate.
What we stock
Ratings from 50 °F down to 10 °F, in mummy, rectangular and XL cuts, from Ozark Trail, Klymit, KingCamp and Tesleader.