Technical Data for Sleeping Bags

In this article, we look at the temperature ranges of sleeping bags, such as minimum, comfort, limit or extreme.

Sleeping bags, an essential item for your adventures. Photo: Korkuerika

Heat capacity is not the only factor to consider when shopping for a sleeping bag. Weight, materials, compressed volume, size, shape, women or men’s versions or how they combine with inner bags to multiply warmth, are also important. Most of these factors are interrelated, and each one is important.

We also talk about these factors in our article on, How to choose your sleeping bag for mountaineering. How to choose a sleeping bag for mountain activities.

An essential feature that is often overlooked when choosing a sleeping bag is the heating capacity. This is expressed as the temperature range.

The temperature range usually appears as "comfort temperature", " limit temperature" or "extreme temperature".

Many are unaware just how reliable this data is, providing the sleeping bag is EC-approved, and has passed tests by authorised laboratories.

In fact, the temperature range is very precise and is a useful tool for choosing the most suitable sleeping bag for your needs. It also allows you to compare sleeping bags with different weights, materials or volume, so that you can select the lightest model with the same performance.

However, there are few who really know how to interpret these labels.

Let us explain.

Sleeping bag label indicating the temperature range, EN standard and the capacity of the compression sack.

How do I Know if a Sleeping Bag Complies with European Standards?

Firstly, you need to know if the sleeping bag has passed the CE tests, according to the EN 13537 standard.

The label showing the temperature range should also show the EN 13537 standard, or the original (not fake) CE mark.

However, this is not a mandatory standard and some sleeping bags, especially by low-end brands, include the comfort, limit and extreme temperature label, in spite of the product not passing the tests or being standardised by the EN standard. This leads to confusion, because their performance is likely to be lower than that shown on the label. Even some of the best brands only use this system in their top range and not in their more economical, lower ranges. So ensure you always look for the EN standard and CE markings on the label.

Why is this Test not Compulsory?

Because sleeping bags are not PPE (Personal Protective Equipment). It is a very strict test and only those brands who are certain they will pass, voluntarily decide to offer customers a guarantee of the quality of their equipment, with an official test.

This European criteria means that all brands that adhere (and practically all quality brands adhere to it, at least for their top-of-the-range bags) will have the temperature range established by an approved independent standard laboratory, using complex tests that we will explain later.

In this way the customer is able to compare sleeping bags by different brands, as well as having reliable and useful information to choose the model with the most suitable heating capacity.

Sleeping bags for extreme temperatures (below -25°C) and for military use are excluded from the standard.

And last but not least: the standard is European, but it is also adopted by many large non-European manufacturers. In the USA, the ASTM F1720 standard has also been created, but it is not widely used at the moment. The University of Arkansas has announced the forthcoming creation of a temperature comparison table between the two.

What is the European EN 13537 Standard?

This standard was created in 2002 to unify criteria for the classification of sleeping bag temperatures, and came into force on 1 January 2005. In 2016, it was further developed into ISO EN 23537:2016, which is currently in force.

After the relevant tests are carried out, in approved and standardised laboratories, a label is created for each model, which is printed or stitched to the sleeping bag, indicating:

  • Extreme temperature
  • Comfort limit temperature
  • Comfort temperature
  • Maximum temperature (optional)

How are the Tests Carried Out?

They are carried out by 3 European laboratories, to which some American laboratories are being added.

All the technical issues related to how the test is performed are included in the ISO 23537 standard.

Testing is carried out on an electronic mannequin with temperature sensors and heaters, so that it simulates the heat felt and emitted by a human body.

  • The manikin is placed inside the sleeping bag, on an insulated mat.
  • It is dressed in a thermal base layer
  • The manikin is heated to body temperature.
  • External temperature conditions are simulated in the room.
  • Measurements are taken over several hours, simulating heat loss during sleep, and indoor/outdoor heat/cold conductivity.
  • This is gives just a general idea of the test, as it is much more complex and detailed (as we said, there are only 3 approved European laboratories), and involves many other specifications, from the size of the sleeping bag, heat systems and sensors, time, room where it is performed, external temperatures, to the posture of the mannequin (relaxed, shrunken, etc.). There are many other factors, all of which can be found in ISO 23537.

    What do the Temperature Ranges Obtained from the Tests Mean?

    Based on the results, the temperature range of each sleeping bag is specified, with the understanding that:

    • Maximum temperature: Is the temperature at which an average man can sleep without excessive sweating. It is set up with the zips open and hood off, and with the arms outside the sleeping bag. The maximum temperature is often not provided on a sleeping bag
    • Comfort temperature: The temperature at which an average woman can sleep comfortably in a relaxed position.
    • Comfort limit temperature: The temperature at which an average man can sleep for 8 hours in a curled-up position.
    • Extreme temperature: The minimum temperature at which an average woman can survive for 6 hours without any risk of death from hypothermia, although frostbite is possible.

    This classification assumes that:

    • The user sleeps on an insulating mat.
    • The user sleeps in a tent to protect against the wind, moisture, etc.
    • The user sleeps is wearing a layer of thermal underwear.

    What is an Average Male or Female, According to the Standard?

    • Average male: 25 years old, height 1.73m, weight 73 kilograms.
    • Average female: 25 years old, height 1.60m, weight 60 kilograms.

    The reason for this differentiation is because medical studies indicate that women are, on average, 5°C more sensitive to cold. This is why women-specific sleeping bags are made: in addition to adapting to the body shape, they provide special protection in areas such as the feet.

    On this, we recommend you visit the article mentioned at the beginning, How to choose your sleeping bag.

    How to Interpret the Data

    Once you know what the temperature range data means, you need to be aware of your own sensitivity to cold.

    It is clearly helpful to have an understanding of how to interpret temperature range data. But it is also important to know how your body responds to the cold and this is learnt through experience.

    If you are a man with a fairly high tolerance to cold, for example, and you know that the comfort temperature indicated on the label refers to an average woman, who is also generally more sensitive to cold than an average man, this provides an indication that it is highly likely to be too warm, if you use it in the high comfort temperature zone, and that you will probably be able to use it at lower temperatures than those indicated, with a certain degree of comfort. So, those who are aware of their own level of tolerance to the cold, are able to interpret the temperature range specifications and decide which is required for the type of activity in question.

    You can also compare it with sleeping bags that you have previously owned, providing they were subjected to the test and have the standard. Once you know how to apply your own parameters to the label categorisation, it becomes easier, and any sleeping bag with the label can be compared to each other with the same system.

    Other issues also come into play, such as cold weather habits or physical condition and it is also important to bear in mind the factors below:

    • Young people produce more heat than older people. The test is carried out on an optimal case of 25 years.
    • People with a higher percentage of fat are better protected against cold.
    • In the mountains your nutrition and hydration is not usually as regular or as suitable as at home, which makes you feel colder.
    • The exhaustion you suffer during the day also makes you feel colder, until your body recovers.

    As you can see, if you know what the label means, and how your body reacts to the cold, it is easy to deduce how much heating capacity a particular sleeping bag will provide.

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