Sleeping Bag Temperature Explained

When looking at sleeping bag temperature ratings there are two main measures to consider: the EN test results (European standard), and the manufacturer’s minimum temperature rating (assessed by the brand). This page explains both, to help you decide whether or not a particular sleeping bag is both safe and suitable for your intended destination.


1. EN Temperature Ratings

2. Minimum Temperature Rating

1. EN Temperature Ratings

In Europe there is a standard temperature rating system for sleeping bags, devised in 2002, and updated in 2012, under the title EN 13537. Designed to regulate European sleeping bag manufacturers and provide a coherent rating system for their customers, the EN 13537 standard measures the following four temperature ratings. During the test, the ‘thermal dummy’ is dressed in two-piece clothing with specific thermal insulation, (i.e. a warm base layer top and trousers), and in knee-high socks with a specific thermal insulation:

Upper Limit: the highest temperature at which a standard adult man could have a comfortable night’s sleep without sweating excessively. This is measured with zips and hood open, and arms outside of the bag.

Comfort: the temperature at which a standard adult woman can expect to sleep comfortably in a relaxed position. This rating is based on a standard woman, as a standard women has a lower tolerance to the cold than a standard man.

Comfort Limit: the temperature at which a standard man can sleep for eight hours in a curled position without waking. This rating is the lower threshold for an undisturbed night’s sleep.

Extreme: the minimum temperature at which a standard woman can remain for six hours without risk of death from hypothermia. At this temperature sleep will be severely disturbed, and frostbite is possible.

In the EN regulations, it is assumed that tested subject can make the best of the sleeping bag by adjusting his position and minimising thermal loss, that he knows limiting factors of sleeping bag and he can protect himself from them.

If a sleeping bag has been EN tested we will provide a graphic showing its EN temperatures ratings, in the above format. The majority of the bags that we sell will have EN temperature ratings. However, the EN test does not produce accurate temperature results for bags containing more than 800 grams of down – so our brands’ warmest bags have not been EN rated. In these cases, consult the minimum temperature rating, explained below.

2. Minimum Temperature Rating

In addition to the EN ratings, most sleeping bag manufacturers provide their own advisory minimum temperature for a safe night’s sleep. This can be based upon a number of criteria, including BS TOG results (another temperature-rating test), and the real-life experiences of their extreme athletes and users. This temperature rating can vary by a few degrees from person to person, depending on factors such as body type, age and gender. Rab call their advisory minimum temperature the ‘Rab Sleep Limit’, Mountain Equipment call it the ‘Sleep Zone’, and Marmot simply call it ‘Bag Temperature’. To simplify comparisons between brands and different sleeping bags, we include this rating in the product image of every sleeping bags we sell, enabling you to compare them quickly and easily. You’ll find it in the box labelled ‘COMFORT’, or ‘MIN TEMP’, as seen below:

Minimum Temperature Icon

The Minimum Temperature should be treated as a safer alternative to the EN Extreme rating in establishing the lower end of a sleeping bag’s safe temperature range. Therefore, when you’re shopping for a sleeping bag, be sure that its minimum temperature rating is comfortably lower than the lowest temperature you’re likely to encounter at your camping destination. For example, if you’re going somewhere where the temperature could drop to -2°C, be sure to buy a sleeping bag with a minimum temperature rating of -2°C or preferably lower.

If in doubt, as with all sleeping bag temperature ratings, always err on the side of caution, because if you’re too hot you can always unzip; whereas if you’re too cold you’re doomed to a chilliy and restless night, or worse. If you know that you suffer from the cold, it’s highly advisable to add 3-5°C on to all temperature ratings, to take this into account.