Sleeping bag temperature ratings can be confusing. A bag labeled “20°F” might keep one person cozy and leave another shivering. Understanding what ratings mean helps you choose a bag that keeps you warm on your trips.
This guide explains sleeping bag temperature ratings, insulation types, shapes and tips for sleeping warmer.
Standardized Temperature Ratings
Many manufacturers test sleeping bags using standardized methods:
- EN 13537: An older European standard.
- ISO 23537: The international standard that replaced EN 13537 in many markets.
These tests use a heated mannequin in a controlled environment to estimate warmth. They provide a consistent way to compare bags across brands that use them.
The Ratings
Standardized ratings typically include:
- Comfort rating: The temperature at which a “standard” person who sleeps relatively cold may sleep comfortably in a relaxed position.
- Limit rating (lower limit): The temperature at which a “standard” person who sleeps relatively warm may sleep curled up for several hours without feeling cold.
- Extreme rating: A survival rating indicating risk of hypothermia. It is not a comfort target. Some newer labels omit or de-emphasize it.
Many bags are named after their limit rating, so a “20°F bag” may be comfortable only at warmer temperatures. Check the comfort rating.
Why Ratings Vary for Individuals
Ratings assume a standard sleeper wearing a base layer on a pad with a certain insulation value. Real comfort depends on:
- Metabolism and whether you sleep warm or cold
- What you eat and drink before bed
- Clothing you sleep in
- Your sleeping pad. See our sleeping pad buying guide.
- Shelter, wind and humidity
- Fatigue
Choosing a Temperature Rating
- Look at the expected nighttime lows where you camp, including elevation effects.
- Choose a bag with a comfort rating at or below those lows if you sleep cold.
- For car camping, you can bring extra blankets or a second bag.
Rough Categories
| Category | Typical Limit Rating |
|---|---|
| Summer | About 35°F and above |
| Three-season | About 10°F to 35°F |
| Winter | Below about 10°F |
These categories are approximate and vary by brand.
Down vs. Synthetic Insulation
Down
- Pros: Excellent warmth for its weight, compresses well, durable with care
- Cons: Loses insulation when wet unless treated, more expensive
Fill power measures down loft. Higher fill power means more loft per ounce. Some down is treated for water resistance.
Look for certifications like the Responsible Down Standard (RDS) if animal welfare matters to you.
Synthetic
- Pros: Retains more insulation when damp, often less expensive, easy to care for
- Cons: Heavier and bulkier for the same warmth
For car camping, weight matters less, so synthetic bags can be a practical choice.
Bag Shapes
- Mummy bags: Tapered for warmth and efficiency. Less room to move.
- Rectangular bags: Roomy and comfortable, often unzip into blankets. Less thermally efficient.
- Semi-rectangular: A compromise.
- Double bags: Designed for couples.
- Quilts: Open-backed designs that rely on the pad underneath.
Features to Consider
- Hood: Adds warmth for your head.
- Draft collar and zipper draft tube: Reduce heat loss.
- Zipper quality: Snag-free zippers are less frustrating.
- Length: Choose a length that fits your height.
Tips to Sleep Warmer
- Use an insulated pad. The ground steals heat.
- Wear dry base layers to bed, not the clothes you wore all day.
- Wear a warm hat.
- Eat a snack before bed.
- Stay hydrated, but empty your bladder before sleeping.
- Use a liner to add warmth.
- Fill a water bottle with hot water, seal it well and place it in the bag. Make sure the bottle is designed for hot liquids.
- Add a blanket over your bag when car camping.
- Avoid breathing into your bag, which adds moisture.
Caring for Your Sleeping Bag
- Store loosely in a large storage sack, not compressed.
- Air it out after each trip.
- Wash sparingly following manufacturer instructions, using appropriate cleaners for down or synthetic fill.
- Use a liner to keep the bag cleaner.
Pairing With Shelter
A good tent keeps wind and rain off your sleep system. See best 4-person tents and how to pitch a tent in the rain.
Understanding Bag Labels
A typical label may show a comfort rating, a limit rating and sometimes an extreme rating, along with the test standard used. When comparing bags, make sure both use the same standard, since non-standardized ratings from different manufacturers may not be directly comparable. If a bag does not list a standard, treat its temperature rating with caution.
Sleeping Bags for Kids
Children may need bags sized for their height, since extra space in an adult bag can be harder to warm. Check that kids’ bags are rated for the temperatures you expect, and pair them with a pad. Bring an extra blanket and dry pajamas, since kids often get damp or cold during the day.
Layering Your Sleep System
For car camping, you can build a flexible system from several pieces: a sleeping bag, a liner, a blanket and a warm pad. On warm nights, unzip the bag and use it as a quilt. On cold nights, add the liner and a blanket. This approach lets you camp comfortably across seasons without buying several bags.
Questions to Ask Before Buying
- What are the typical nighttime lows on your trips?
- Do you sleep warm or cold?
- Do you prefer a roomy rectangular bag or a snug mummy bag?
- Will you also use the bag for backpacking?
Down Care Tips
If you choose a down bag, keep it dry with a waterproof stuff sack, air it out each morning when conditions allow and wash it only when needed using a cleaner designed for down. Dry it slowly on low heat with clean dryer balls to help restore loft, following the manufacturer’s instructions.
Frequently Asked Questions
What does a 20-degree sleeping bag mean?
Often that the bag’s limit rating is about 20°F. Check the comfort rating for a better sense of real-world warmth.
Should I choose comfort or limit rating?
If you sleep cold, use the comfort rating. Warm sleepers may find the limit rating closer to their experience.
Is down or synthetic better for car camping?
Both work. Synthetic is often less expensive and handles dampness better, while down is lighter and more compressible.
Why am I cold in a warm sleeping bag?
Your pad may not insulate enough, or you may need dry layers or a hat.
How should I store a sleeping bag?
Loosely in a large, breathable storage sack.
The Bottom Line
Sleeping bag temperature ratings help you compare bags, but they are estimates. Look at comfort ratings, consider whether you sleep warm or cold, and pair your bag with an insulated pad. Choose down or synthetic based on budget and conditions, and use simple tricks to sleep warmer.
Editorial note: Camp Craftly is independent and reader-supported. This guide is based on research into manufacturer documentation, published specifications and widely accepted best practices; we have not been paid to mention any product. If we add affiliate links in the future, they will be clearly disclosed per our Affiliate Disclosure.