The coldest time of the day is said to be just before sunrise – because the earth has had all night to drive out the previous day’s heat. This is the time when your choice of sleeping bag will either get you in trouble or keep you snugly asleep.
So how do you choose the right sleeping bag for you, one which can handle the many variables affecting warmth when you go camping, hiking or mountaineering?
The EN Standard for sleeping bags
The most recognised standard currently available for testing sleeping bags is the European Norm (EN) 13537 protocol. It’s widely accepted in the industry – allowing more accurate comparisons between sleeping bags (and between brands).
Based on extensive research, the standard translates insulation value into a range of temperatures.
Your body and ‘level of sleep comfort’ is different from others, so it’s important to treat the EN temperature ratings as a guide. Also, be aware of the different temperature ratings for females and males as women are generally colder than men.
How sleeping bags are tested
During EN testing, a dummy with a human shape and a heated body surface (a thermal manikin) is dressed in a two-piece suit – essentially long sleeve thermal underwear and knee length socks.
The manikin is then placed inside the sleeping bag that needs to be tested, moved into a climate chamber and positioned on a sleeping mat.
The air in the climate chamber and on the surface of the manikin is measured using heat sensors. These numbers then determine the insulation value of each sleeping bag.
EN temperature ratings
Temperature ratings are designed to give you an indication of a sleeping bag’s performance. Here’s how we, at Kathmandu, show the EN Standard temperature ratings on our sleeping bags.
The thermal manikin test produces three relevant temperature ratings, which we display as:
- T Comfort – a standard woman can expect to sleep comfortably at this temperature.
- T Lower limit – a standard man can still get a comfortable night’s sleep at this temperature.
- T Extreme – a standard woman can still survive a night at this temperature, though there’s a risk of hypothermia.
Factors affecting sleeping bag warmth
Sensitivity to temperature is quite personal. There are many variables that affect how warm you’ll be inside a sleeping bag. Those factors can include your:
- Sensitivity to temperature
- Conditioning, fitness and level of experience
- Gender and age
- Sleeping habits
- Hunger and nutritional intake
- Level of exhaustion; and
There are other reasons for your level of comfort inside a sleeping bag, such as your sleepwear, sleeping mattress, and prior exposure to wind, rain, snow and humidity.
Remember to treat the EN temperature ratings as a guide. Speak with our in-store staff and use your best judgement when choosing a bag to meet your needs.