Understanding Sleeping Bag Temperature Ratings

Two backpackers camping on a rock ledge with warm 4-season sleeping bags, a testament to the importance of understanding sleeping bag temperature ratings

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Selecting a sleeping bag can feel pretty puzzling, especially when you hear about something called “sleeping bag temperature ratings.”

In this article, we’ll clarify what sleeping bag temperature ratings are, why they matter, and also point out their drawbacks.

We promise that by the time you finish reading this, you’ll be all set to pick out the ideal sleeping bag for your next outdoor journey.

Sleeping Bag Temperature Ratings Explained

When backpackers are shopping for a sleeping bag, they mainly consider three things: the price, how well it keeps them warm, and how much it weighs. Figuring out how warm a sleeping bag is can still be quite confusing, and it’s just as challenging as ever.

In the past, it was easy to judge a sleeping bag’s warmth only by its fill weight. As synthetic materials gained popularity, numerical temperature ratings were introduced. However, these ratings varied between brands, and inaccurate claims became a problem.

Cheaper sleeping bags flooded the market with seemingly fabricated temperature ratings, making it hard to distinguish them from pricier, specialized options.

The sleeping bag industry improved things by introducing a testing standard: The EN (European Norm) 13537 standard, “Requirements for Sleeping Bags,” was established in 2002, making it easier for consumers to compare sleeping bags from different brands. Outside of Europe, this standard is now known internationally as ISO 23537.

While not legally enforceable, the EN/ISO standard offers a means to report manufacturers who provide highly misleading temperature ratings.

Understanding Temperature Ratings

Manufacturers use the EN/ISO standard to tell you how warm or cold it feels inside a sleeping bag when you’re wearing just base layer thermals. To determine this, thorough tests in a lab using a dummy are conducted.

During these tests they take into account how fast your body burns energy, what kind of clothing you’re wearing inside the bag, and how much the bag will be exposed to wind and moisture.

The result of all this scientific exploration? It’s those standardized three sleeping bag temperature ratings: Comfort, Limit, and Extreme.

Temperature Rating Categories Explained:

Example sleeping bag temperature ratings EN tag

Example EN/ISO sleeping bag tag.

  1. Comfort: This is the temperature for a comfortable night’s sleep for the average woman wearing one base layer and sleeping in a relaxed position.
  2. Limit (Main Rating): This rating, typically displayed prominently on the product label, represents the lowest temperature at which the average man can sleep comfortably. It’s a useful reference for campers but may require extra layers or a warmer bag if exceeded.
  3. Extreme: This rating is for survival situations, indicating the lowest temperature a sleeping bag is designed for the average woman. You can pretty much ignore this number unless you have a masochistic bent.

These differences in ratings happen because many women tend to experience a greater drop in their internal body temperature during the night compared to men.

Temperature Ratings in Practice

The manikins used in EN/ISO tests resemble a human but can vary between testing labs. The problem is that if the sleeping bag has snug spots around the manikin, it squashes the insulation, making the bag seem colder than it truly is. A real person can shift around to stay warm, but the manikin can’t.

Keep in mind that the test usually rates roomier sleeping bags higher, while those with a tailored or slim fit tend to get lower scores. So, unless the manikin matches your size accurately, the warmth provided by the sleeping bag may not be what you expect.

Furthermore, it’s important to note that not all sleeping bags have an EN/ISO rating. This test standard doesn’t apply to bags made for extreme cold or kids’ bags. In some cases, brands might decide not to get EN/ISO testing for bags meant for mild conditions or casual use.

When you come across a “temperature rating” specification that isn’t labeled as either “comfort” or “lower limit,” it’s likely just the brand’s estimate, not a result of a standardized test. In such cases, use that specification as a rough guideline.

So, how can you make sure you stay warm when you’re out there? When you’re shopping for a sleeping bag, it’s a good idea to aim for one that’s rated about 10 degrees Fahrenheit (5°C) warmer than what you think you’ll need.

In our view, if you’re an ultralight backpacker, you should use this rough temperature estimate to help you discover the perfect sleeping bag your needs:

  • 3-Season Sleeping Bags: Limit temperature 30°F and above.
  • 4-Season Sleeping Bags: Limit temperature 15°F and above.
  • Winter Sleeping Bags: Limit temperature 15°F and below.

Ideal Sleeping Bag: Beyond Temperature Ratings

A camper enjoying their evening meal while understanding the importance of sleeping bag temperature ratings

When choosing the ideal sleeping bag for your outdoor adventures, sleeping bag temperature ratings are just one factor. Now, let’s delve into other essential considerations:

Fill Material: Sleeping bags come with two primary types of insulation: synthetic and down:

  • Synthetic insulation is durable and retains warmth even when wet, making it suitable for moist conditions. However, it doesn’t compress as well as down, which means it takes up more space in your backpack.
  • Down insulation is lightweight and highly compressible, making it a favorite for ultralight backpackers. However, it’s more expensive and loses insulation when wet.

Fit and Comfort: The fit of your sleeping bag is as important as its temperature rating. A well-fitting bag enhances comfort and ensures a good night’s sleep. There’s no one-size-fits-all formula for the perfect fit, as height and weight vary among individuals. Look for a bag that provides enough room for your arms and doesn’t constrict your waist, hips, or shoulders. A snug but not overly tight fit is ideal.


Knowing how to interpret sleeping bag temperature ratings is an essential part of having a great time during your outdoor journeys. Once you grasp the ins and outs of the EN/ISO rating system, you’ll be in a good position to pick the right sleeping bag.

Whether you’re heading out for a cold mountain expedition or a cozy summer camping adventure, your sleeping bag will be like a reliable friend. To ensure you stay comfy, it’s a good idea to choose one that’s rated about 10 degrees Fahrenheit (5°C) higher than what you expect you’ll require for a peaceful night’s sleep.

Looking for a ultralight sleeping bag? Check out our TOP 5 Guides for the lightest 3-season, 4-season and extreme cold winter sleeping bags on the market.


Can you use a 20 degree sleeping bag in the winter?

Using a 20-degree sleeping bag in winter depends on various factors. While it can keep you warm in moderately cold conditions, it may not suffice for extreme winter weather. Winter temperatures can vary significantly, and factors like wind, humidity, and your own cold sensitivity play crucial roles. It’s advisable to choose a sleeping bag with a lower temperature rating for added safety. Additionally, wearing appropriate clothing and using insulating sleeping pads can help boost the bag’s performance.

What is the difference between comfort and limit temperature?

The difference between comfort and limit temperatures in sleeping bag ratings is crucial. The comfort temperature signifies the temperature at which the average female camper can anticipate a comfortable night’s sleep with one layer of base clothing. Conversely, the limit temperature is based on the lowest temperature at which the average male camper can expect comfort and is typically the primary rating displayed on the product. If you encounter conditions colder than the limit rating, it may be necessary to add extra layers, employ a sleeping bag liner, or opt for a warmer-rated bag.

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