Measuring and stating the temperature span of a sleeping bag is very complex. Basically we generate heat through our metabolism – and in a sleeping bag we loose heat through conduction to the ground, convection via air circulation, respiration from the air we exhale, evaporation of sweat and radiation of infra red heat, where the two former are the most important.
For comfortable sleep we must have heat balance, which is the difference between the heat generated and the heat lost through the above mentioned factors.
All these again depends on the metabolic heat output which is a very complex issue involving body fat index, age and gender – but also experience and lifestyle influences the sense of warmth. Younger persons generally produce more body heat than older ones, a fat person often feels warmer than a thin person, experienced lose less warmth than rookies – and women are generally colder than men.
All Nordisk sleeping bags are tested according to the EN 13537 standard which defines the temperature by which you are guaranteed a full nights comfortable sleep without waking up from being cold.
The comfort temperature is for men the highest temperature at which you can sleep without sweating intensively defined with the ventilation zippers open, arms outside the bag and the hood open. It is also the lower limit for the average woman and according to EN 13537 this value is 5º C higher than for a standard man.
The limit temperature is defined as the lowest temperature at which a person has a good nights sleep without waking from being cold. It is also the lower limit for the average man.
The extreme temperature is the lower limit for risk of health damage, and is the lowest temperature at which the sleeping bag protects the user from hypothermia.
Did you know...?
There are several standards for testing sleeping bags that all are based on a standard person, but in reality such a person does not exist, and since they test differently the also result in different values. So which of the sleeping bags below is the warmest?
EU Norm: -4°C (EN 13537)
French Norm: -8°C (limit comfort)
Norwegian Norm: -10°C (Thelma comfort)
British Norm: -11°C (854785)
US Norm: -16°C (ASTM F1720)
The correct answer is that they are all the same!