When stating the temperature range in our sleeping bag advice, we use European standard EN 13537, which creates a comparable standard and provides a basic guide to the heat performance of our sleeping bags.

How we test: A calibrated, thermal, articulated “adult” dummy is put inside the test sleeping bag, which is then placed in a climate chamber with a standardised environment. As the horizontal areas of the doll are subjected to specific heat output, sensors measure the temperature difference between the internal and external surface over several hours. The respective temperature range is calculated from the results.

THE TEMPERATURE RANGES

• T(COM) Comfort: indicates the lower temperature limit at which a standard woman (25 years / 60 kg / 1.60 m) can comfortably sleep through one night. Even an inexperienced user will feel completely comfortable at all times in this range.
• T(LIM) Lower Limit: indicates the lower temperature limit at which a standard man (25 years / 70 kg / 1.73 m) can comfortably sleep through one night. In order to stay warm, in this range the user may have to adapt to the conditions through clothing and behaviour.
• T(EXT) Extreme: indicates the lowest extreme temperature which a standard woman can tolerate for 6 hours in extreme cold. There’s no chance of sleeping here. In the extreme range, you can expect to feel very cold.  Hypothermia poses a risk to health.

Other temperature factors that are crucial when choosing the right sleeping bag:

These standardised indications only provide laboratory values. They are designed to ensure good comparability between products from various manufacturers. Everybody is built differently and reacts individually to certain conditions, so this information can only act as a guide to a purchasing decision. Things to consider include: 

1. People have more heat-determining factors than a “dummy” in a climate chamber. For example - the different perception of temperature by men and women; age, fitness, as well as experience. Other factors influencing heat performance include fatigue levels (exhausted versus well-rested), but also a lack of food or an excess of alcohol (which makes you get cold faster).
    
2. External circumstances that are “normed” in the climate chamber play a key role in real life and contribute to the optimal use of the “heat performance”.
    
3. A good sleeping mat will insulate the sleeper from the ground.
    
4. Functional underwear that is dry and can wick moisture away (including a hat!) plus a sheltered sleeping area are important, as wind and moisture significantly impair restful sleep.
    
5. The standardised measured values are determined in the climate chamber. Please bear in mind that multi-day activities or difficult natural conditions have completely different requirements, so it is necessary to prepare for the relevant conditions.

However, the right sleeping bag is only half the story - it is also important where, on what and how you sleep!

• Sleeping mat: Cold ground or circulating air will draw heat away from the body even through the best sleeping bag! This heat transfer should definitely be prevented by using a well-insulated mat.
   
• Wind protection: wind chills you! The wind chill factor means that the body perceives +5°C in a light breeze (25 km/h) as 0°C. A tent, bivouac sack or even a boulder can protect you against a highly chilling air exchange (B). Locate your sleeping area somewhere that is well protected from the wind.
   
• Functional underwear: The heat of the sleeping bag can be easily maximised by wearing warm, long functional underwear and socks. Dry clothing on the feet also ensures additional insulation.
   
• Hat: in your sleeping bag, your head or face are the only contact to the chilly outside world. A cold head makes the rest of the body lose heat too. A hat, perhaps even a balaclava, offers very effective protection against the cold.
   
• Enough food: The body needs lots of energy when climbing, hiking, cycling, etc. Anyone who fails to top up their energy reserves by not eating enough will not be able to produce enough heat and will get cold faster.
   
• Enough liquid: Drink enough during the day, as the body stops being able to produce enough warmth when it is dehydrated. Before going to bed in your sleeping bag, a cup of tea or hot chocolate is a good way of warming you up.
   
• Avoid alcohol: Do not drink too much alcohol in cold temperatures. Alcohol initially creates a warming sensation, but when it wears off, you feel the cold even more.
   
• Keep everything dry: Clothing and sleeping bags, especially down ones, have a lower insulation value when they’re wet than they do when dry. The supposedly warm socks that you were wearing get cold very quickly due to evaporation. Avoid getting into your sleeping bag with your sweaty clothing on. A change of clothes will stay dry in a watertight packsack. And whenever possible, leave your sleeping bag to air – for example, over the tent.