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The European Temperature Standard

EN 13537 is a European standard designed to standardize the temperature ratings on sleeping bags manufactured and/or sold in Europe. The standard also defines how sleeping bags must be tested and rated. EN13537 applies to all sleeping bags with the exception of sleeping bags for military use and sleeping bags for extreme temperatures (i.e. below -25°C).
The EN Standard 13537 is in effect since 2002 – and since 2005, all new sleeping bags offered in the marketplace must be EN tested.

How sleeping bags are tested according to EN 13537
For EN 13537 temperature tests, a life-size mannequin (based on a “standard man” and “standard woman" of average age, weight, and height) with heaters and temperature sensors is dressed in one layer of long underwear and a hat. It is placed inside the sleeping bag being tested. The bag is laid on an insulating sleeping pad inside a climate-controlled chamber. The mannequin is heated to simulate body warmth, and measurements are taken of the air in the climate chamber and the surface (“skin”) of the mannequin. From these measurements, the insulation value of the sleeping bag is determined. These calculations provide four EN temperatures ratings:

  • Upper Limit (Tmax): the temperature at which a standard man can sleep without excessive perspiration. The range between Tmax and Tcomf is considered the "Comfort Range."
  • Comfort (Tcomf): the temperature at which a standard woman can expect to sleep comfortably in a relaxed position without being cold. The range between Tcomf and Tlim is called the "Transition Range."
  • Lower Limit (Tlim): the temperature at which a standard man can sleep for eight hours in a curled position without waking. The range between Tlim and Text is also known as the "Risk Range."
  • Extreme (Text): the minimum temperature at which a standard woman can remain for six hours without risk of death from hypothermia (though frostbite is still possible).

Temperature Standard vs. Personal Feeling
Sensitivity to temperature is a very subjective matter, depending on several factors like gender, level of exhaustion, nutritional condition, sleeping habits, or blood alcohol. But there are also several objective factors responsible for each individual’s comfort inside a sleeping bag:

  • Wind exposure
  • Quality of the sleeping mat (the layer between the ground and the sleeping bag)
  • Humidity

Once you realize all these factors, it becomes plausible why some people may perceive the same measured temperature in different ways. When buying a sleeping bag, this should be taken into account in addition to the rating stated on the hangtag.