How to Choose a Sleeping Bag: Temperature Ratings, Fill Power & Shape
Temperature ratings are frequently misunderstood — here is how to read them correctly and match a bag to your actual conditions, insulation type, and budget.
Transparency notice: TrailNestCo is reader-supported. When you buy through links on our site, we may earn an affiliate commission at no extra cost to you. This never affects our rankings. Learn more →
A sleeping bag is one of the few pieces of gear where getting the spec wrong directly ruins a trip — too warm and you're sweating and sleepless; too cold and you're miserable or, in bad cases, at real risk.
Step 1: Understand temperature ratings
The EN/ISO standard gives three numbers: a comfort rating (where average cold-sleepers stay comfortable), a lower limit (average warm-sleepers, curled position), and an extreme rating (survival only — never a comfort target).
Buy for the comfort rating, not the lower limit, and add a 10–15°F buffer for unpredictable conditions.
Step 2: Choose insulation type
Down: best warmth-to-weight ratio and compresses small — but loses warmth when wet (unless hydrophobic-treated) and costs more.
Synthetic: keeps insulating when wet and costs significantly less — but is bulkier and heavier for equivalent warmth.
Down suits dry, cold conditions where pack weight matters. Synthetic wins for wet climates, water proximity, or tight budgets.
Step 3: Pick the right shape
Mummy: warmest and lightest, least room to move. Semi-rectangular: a good balance. Rectangular: roomiest and heaviest, lower warmth — but car campers often prefer them, and some zip together.
Backpackers should favor mummy or semi-rectangular; car campers prioritizing comfort often go rectangular.
Step 4: Check fit and length
An oversized bag traps excess air your body has to heat, reducing effectiveness. Choose regular or long sizes based on height with a few inches of margin — not exact measurements.
Step 5: Match the bag to trip type
- Summer car camping: 35–50°F rating, either insulation.
- 3-season backpacking: 15–30°F, down preferred.
- Winter/shoulder-season: 0–15°F or lower, hydrophobic-treated down.
Frequently asked questions
What temperature rating do I need?
Pick a bag rated 10–15°F below the coldest temperatures you expect, using the comfort rating — not the lower limit.
Down or synthetic — which is better?
Down wins warmth-to-weight and packability; synthetic performs better wet and costs less.
Explore more
More from Camping & Outdoor
Independent editorial research. Zero pay-to-play.