Temperature Ratings for Sleeping Bags

The modern sleeping bag is designed with the rugged outdoor explorer in mind, taking into account his will to endure all but the most rigorous of conditions, including that of abominably low temperatures.  To the seasoned sleeping bag user, cold isn’t just cold – there are varying degrees of it, ranging from “mild chill” to “freaking frostbite.”  To keep their patrons from freezing their toes off, sleeping bag companies have built their bags to withstand different degrees of shivering weather, assigning them what we have come to refer as "temperature ratings." 

The typical sleeping bag will come with two different ratings:  the Comfort Temperature Rating and the Extreme Temperature Rating.  The first value is a range of the ambient temperature in which you are expected to sleep comfortably in the sleeping bag without it being too warm or too cold.  The second value is a single number that represents the absolute coldest it can be before the bag becomes ineffective as a sleeping device.  Sleeping bags today are often marketed with only the Extreme Temperature Rating displayed, to give the buyer a good idea of the bag’s upper limit.

 

According to the manufacturers, these ratings are obtained from extensive testing, which mostly involves sticking a poor unfortunate volunteer in an experimental bag and subjecting him to increasing drops in temperature until he registers discomfort.  As such, these ratings are not to be taken as absolutely certain.  Every person has a different tolerance for extreme temperatures, owing to metabolism, body fat and other factors.  Gender is particularly important, as men can normally handle tolerate lower temperatures than women.  Consequently, your experience with the sleeping bag may be better or worse than the rating suggests.  To be on the safe side, use the temperature rating only as a helpful reference, with about five to ten degrees of error room.  This way, you won’t be caught literally out in the cold.

In recent years, sleeping bags sold in the United States have begun adopting a standard rating system, first adopted in Europe, known as the European Norm (EN) 13537 testing method.  This rating takes various nuances into consideration, such as the user's gender, and is the result of independent stringent laboratory tests involving a mannequin and advanced measuring equipment.  As such, the ratings derived tend to have a lower margin of error, and provide a fairly accurate picture of how the sleeping bag would perform outside.  The EN rating consists of three values – a comfort rating, which is the lowest temperature in which a woman can sleep comfortably in the bag, the lower limit rating, which is calibrated towards a man instead, and the extreme rating, which is the lowest temperature in which a woman can survive.  Though EN ratings are more reliable overall, it is still advised not to take the extreme rating too literally.

One must also keep in mind that EN and other temperature ratings assume that the user is wearing at least one base layer of clothing and a hat, and is using an insulating sleeping pad under the bag.  As such, those who like to sleep in the raw should probably adjust those ratings by at least another ten degreees.

Return to Sleeping Bags Guide Home Page

Text copyright 2009 Sleepingbagsguide.com and may not be reproduced without consent. This is not the official web page of any of the products listed on this site, this is a review page created by an individual.