Temperature Rating
Temperature ratings tell you the lowest temperature at which a sleeping bag will keep an average sleeper warm. Look for EN/ISO-tested ratings for the most reliable numbers. If you tend to sleep cold, choose a bag rated 10–15°F below the lowest temperature you expect to encounter. Three-season bags (rated 15–30°F) handle spring through fall in most climates, while summer bags (35°F+) save weight when warmth isn't critical. For winter camping, look for bags rated 0°F or below.
Insulation Type: Down vs. Synthetic
Down insulation offers the best warmth-to-weight ratio and compresses smaller, making it ideal for backpacking. However, down loses insulating ability when wet unless it's treated with a hydrophobic coating (DWR-treated down). Synthetic insulation is heavier and bulkier but continues to insulate when damp, dries faster, and typically costs less. For wet climates like the Pacific Northwest, synthetic or treated down is the smarter choice. For dry alpine conditions and ultralight pursuits, high-fill-power down is king.
Shape and Fit
Mummy bags taper from shoulders to feet, minimizing dead air space for maximum thermal efficiency — ideal for backpackers and cold sleepers. Semi-rectangular bags offer more room to move around and are great for side sleepers and car campers who prioritize comfort. Rectangular bags provide the most space and can often be unzipped into a blanket, but they're heavier and less thermally efficient. Consider your sleeping style and how much room you need to feel comfortable.
Weight and Packability
If you're carrying your bag on your back, every ounce matters. Ultralight bags under 2 pounds exist but often sacrifice durability or temperature range. A good backpacking bag weighs 2–3 pounds with a compression sack that fits inside or straps to your pack. Car campers can afford to go heavier — 4–6 pounds — in exchange for roomier cuts and plusher insulation. Always check both the fill weight and total weight, and consider the compressed volume in liters for pack planning.
Key Features to Look For
Draft tubes behind the zipper prevent cold air from seeping in. Draft collars around the neck trap warm air inside. Hood cinches let you seal heat around your head on cold nights. Full-length two-way zippers add ventilation flexibility. Stash pockets keep your phone and headlamp close. Anti-snag zipper guards save frustration at 2 a.m. Finally, consider storage sacks — always store your bag loosely in a cotton or mesh sack at home, never compressed, to preserve loft over the years.