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What Do the Ratings on Sleeping Bags Mean?

what do the ratings on sleeping bags mean

The ratings on sleeping bags might leave you feeling confused and concerned that you may not be getting exactly what you want or need.

We’ve unravelled the jargon for you so you won’t need a lie down before you’ve even ordered your sleeping bag!

So what do the ratings on sleeping bags mean? In a nutshell:

The ratings refer to the range of temperatures the sleeping bag can offer function. From the maximum temperatures you will be comfortable in, to the lowest temperatures you can survive in.

Reading the following information could mean the difference between hot or cold sleepless nights, sweet dreams, or even staying alive.

What do those acronyms mean?

Acronyms might be convenient to print on a tiny label, but they could really muddy the water if they’re not explained.

Related: The Best Sleeping Bags for Warm and Cold Weather Camping

Here’s to clearing the mud for your next expedition and explaining EN and ISO ratings to help you better understand what sleeping bag you are getting.

EN Standards

EN is the ‘European Norm’ or standard. If a bag has this EN13537 rating on it, it means that you can have confidence that it has been tested by independent laboratories using standardised criteria, making sleeping bag performance easily comparable.

It started in Europe in the early noughties but surprisingly is still not obligatory. If you are travelling the world and pick up a bag, they won’t necessarily have this classification and you might be taking a risk with how suitable your bag is for different temperature conditions.

You might also see EN13537:2002 or EN13537:2012 on your bag. These are updated EN standards to reflect refinements made over the years. 

ISO Standards

ISO is the ‘International Standards Organisation’ which was introduced in 2016. You might see ISO EN23537:2016 on a bag. These standards have been introduced in more countries and are comparable to the EN standards.

Read our guide to the best sleeping pads for backpacking here

What Countries Follow the Standards?

To date, the following countries standardise the temperature ratings on their sleeping bags:

  • Austria
  • Belgium
  • Czech Republic
  • Denmark
  • Finland
  • France
  • Germany
  • Greece
  • Hungary
  • Iceland
  • Ireland
  • Italy
  • Luxembourg
  • Malta
  • The Netherlands
  • New Zealand
  • Norway
  • Poland
  • Portugal
  • Romania
  • Slovakia
  • Spain
  • Sweden
  • Switzerland
  • United Kingdom

How are the Ratings Calculated?

In lab conditions.

The sleeping bag is placed on a sleeping pad with specific criteria, a test dummy is placed and monitored in the bag, wearing only a base layer and a hat.

The tests collect data for an ‘average man’, that is a man of 25 years old, 5’8’’ (1.73m) tall and 10 stone (73kg) heavy. And an ‘average woman’ of 25 years of age, 5’3’’ ( 1.6m) tall and weighing 8.25 stone (60kg).

Are The Ratings Reliable?

It’s still worth noting that even though the EN and ISO standards are based on sound science, it isn’t an exact science.

The tests are still laboratory tests and how the bags perform in the field could vary significantly.

Also, be aware that if a bag states that its comfort temperature is 2°C you might not necessarily think so!

We are all individuals, someone in the same bag could feel freezing at 2°C whereas someone else might think its positively roasting!

There are too many variables on our wild and wonderful planet to know exactly how a sleeping bag will perform in the elements.

Ok, enough of the background. Let’s get down to the nitty-gritty.

What is a Comfort Rating?

When your bag gives a temperature for the comfort rating this is the temperature at which a woman (who generally feels the cold more) feels comfortable, and won’t lose body heat while sleeping.

Comfort ratings are generally found on women’s sleeping bags.

What is a Lower Limit Rating?

This is an indication of the temperature a warmer sleeper (generally men) will feel comfortable sleeping in for a length of eight hours.

Lower limit ratings are generally found on men’s sleeping bags.

What is the Upper Limit Rating?

This is the temperature at which a man can sleep for eight hours without perspiring excessively. It is calculated with the hood down, the zippers open and arms outside the bag.

What is the Extreme Rating?

This is the temperature a woman can survive in for six hours without risk of dying from hypothermia.

It’s not recommended you ever experience temperatures anywhere near this rating in your bag, as it does not guarantee protection from frostbite!!

Do All Bags Have a Temperature Rating?

Some bags don’t have the EN or ISO rating, but instead have one that has been calculated by their own standards. This can be the case when a company makes sleeping bags for casual use or for mild conditions.

Similarly, bags may not have an EN or ISO temperature rating because these tests are not valid when testing bags for children, bags required for extreme weather conditions or for the military.

It makes comparing like for like difficult but it doesn’t mean there’s anything necessarily subpar about the bag. 

What are Season ratings?

Seasons ratings are engineered to inform buyers of a sleeping bag’s general performance potential. The scale ranges from one season to five seasons (huh?).

  • One season – suitable for Summer nights, 10°C or above.
  • Two season – suitable for warmer Spring nights into late Summer, 5°C or above.
  • Three season – Perfect for all environments down to 0°C. Not suitable for frost conditions.
  • Four season – Serious protection for the winter months that will see you down to the – 5°C range.
  • Five season – Extreme equipment suited to expeditions and harsh climates. Protection can go as low as -40°C.

Parting Thoughts

If you are a casual, summer camper then checking the temperature rating on your sleeping bag might not be top of your list of things to do.

Many companies will give a quick description of how many ‘seasons’ your bag will be suitable for and you might feel this is enough for you.

If you are camping in all seasons and know that you will face some varied weather conditions on your adventures then it is highly advisable that you take note of your sleeping bag’s temperature rating.

Check out the coldest temperatures you are likely to encounter on your trip and choose a bag with a comfort rating or lower limit rating at or below that temperature.

There’s nothing nicer than zipping up your sleeping bag confident that it will keep you perfectly warm out in the elements. So be sure you know what to look for and you will not only be able to rate your bag but rate your experience too!

Want more? Check out our guide to the best tents for couples here

See you on the mountain.