Understanding Temperature Ratings

April 27, 2020

SAY WHAT?

Sleeping bag temperature ratings are a somewhat complicated subject - we feel you - Comfort? Extreme? Limit?...... what the hell?

To understand them better, it helps to understand how the bags are tested for warmth in the lab (including some of the limitations in the process), and the meaning of some not-so-intuitive terms you’ll see in Selk'bags temperature ratings.

Here are important things to understand when using temperature ratings to shop for a sleeping bag:

• Lab-tested temperature ratings (as indicated by “EN” or “ISO” ratings) are useful for making an apples-to-apples comparison between sleeping bags from different brands.
• Real-world comfort probably won’t match lab-tested temperature ratings because of all the variables that a lab can’t simulate.

HOW SLEEPING BAGS ARE TESTED

In the old days, brands tested sleeping bags in their own labs using a variety of methods, so there was no way to know if one company’s 30-degree bag was truly just as warm as another’s 30-degree bag.

The bag industry solved this problem by agreeing to test bags the same way for all brands. Today most brands send their sleeping bags to an independent test lab that assigns bag temperature ratings.

EN (European Norm), was the original standard adopted by the sleeping bag industry. Today, a new entity, the ISO (International Standards Organization), oversees bag testing, but the method is almost identical to the EN bag test. 

Standardized laboratory tests produce a rating range for each sleeping bag, with two temperature ratings within that range specifically called out:

• Comfort rating indicates the temperature at which a standard woman wearing nothing but the Selk'bag can expect to sleep comfortably in a relaxed position.
• Lower rating (which is always lower than the comfort rating) indicates the temperature at which a standard man wearing nothing but the Selk'bag can expect to sleep comfortably in a relaxed position. 

KEY TAKEAWAYS TO LOOK FOR

Temperature ratings are estimates, not gospel: Lab testing simulates how a sleeping bag should be used: A sleeping pad is placed under the bag, and a test dummy inside the bag is dressed in base layers. While this protocol ensures that all bag tests are done the same way, it can’t account for variations like differences in people’s clothing and gear (i.e. sleeping pads), differences in body types (warm and cold sleepers), changing weather conditions, differences in food people eat and more. So, when you use your sleeping bag in the outdoors, its comfort level will probably differ from its tested temperature rating.

Why women’s sleeping bags use the comfort rating: Data on physiological differences between traditional genders has always shown that the “average woman” will feel colder in the same bag than the “average man” will feel. So, the comfort rating, which is the temperature for colder sleepers, was the logical spec target for women’s.

Not every sleeping bag has an ISO (or EN) rating: The test standard isn’t valid for bags designed for extreme cold, nor does it apply to kids’ bags. And brands might not choose to get ISO testing on bags intended for mild conditions or casual use. Whenever you see a “temperature rating” spec that’s not stated as either “comfort” or “lower limit,” that bag spec probably reflects the brand’s estimate, not an ISO or EN test. Use that spec as a rough guideline, not a rating you can absolutely compare to similar bags from other brands. On Selk'bag case, you will always see our rating temperatures on the hangtag and on our website so you can check that information at the moment of buying. 

 

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