Two values are particularly important: T _comf  and T _lim

Here is an example of the  Biopod DownWool Subzero :

The first value – T _comf – is the value at which it's just below freezing. This means that T _comf is the lowest value of the comfort range, where it can already get chilly.

The second value – T _lim – is the value at which you can start to feel cold, i.e. start to shiver.

The third value – T _ext – is a theoretical value, at which there is already a risk of health damage due to hypothermia. You don't need to consider this value when purchasing a sleeping bag.

According to EN 23537-1, precise temperature specifications for children's sleeping bags are not permitted! The reason for this is that children vary so much in their development that, for example, even two children of 140 cm height cannot be compared in their temperature sensitivity.

Uniform testing procedure

In order to guarantee neutral comparability of the temperature specifications of sleeping bags, these are determined according to the European standard EN 13537/EN 23537 using a uniform test procedure:

A heated manikin lies in a test sleeping bag in an air-conditioned room. The energy input required to maintain a stable temperature of approximately 20 different body segments is then determined.

Sleeping bag temperature test dummy Karel (Image source: TZU Textile Testing Institute)

Reality check of the temperature value according to standard

Grüezi bag considers this testing procedure to be insufficient: 

• A standard doll cannot be compared to an average human: it is standardized to the age of 25, it does not move in its sleep , does not pull up its feet, and only sleeps on its back instead of on its side.
• The measuring points are on the top of the doll, not on the back, for example.
• In addition, the term "comfort temperature" is misleading: T _comf is the lowest value at which people who are normally sensitive to cold and in good health just do not feel cold. 

The value at comfort temperature is therefore only suitable for people who are young, healthy and fit.

Please allow for a buffer if you generally get cold more easily or are on physically demanding tours and might be exhausted by the evening. Even if the altitude is unusual or the local conditions are less hygienic, your body will perform harder and require more energy. All of this makes you more sensitive to the cold.

Realistic temperature specifications for Grüezi bag sleeping bags

We want happy customers who don't freeze. Therefore, in addition to the EN-ISO standard, we also specify our optimal application range.

• We are very careful with the temperature ratings on our sleeping bags and, for all hybrid and down-wool sleeping bags, we specify a lower rating than the bag's rated capacity. For example, the Subzero: according to the EN test, it reaches -2°C, but we specify a rating of +2°C. This looks worse compared to the competition, but we haven't received any complaints, even from sensitive individuals.
• When comparing sleeping bags, you should always look at the same dimensions (length and width, as well as the amount of down). This is the only way to determine how good or heavy a sleeping bag is. If, for example, the back section is lightly filled and only the top section is heavily filled, then the sleeping bag will have a good temperature rating in the test, but not in real life. This is because when you turn over at night with the sleeping bag in it, your back will be cold with the lower fill level, and the heat will escape during the night. This is why a Grüezi bag sleeping bag is filled equally on the top and bottom. Any perceived difference only comes from the different chamber sizes.
• A Grüezi bag sleeping bag has a comfort cut: real people sleep more soundly when they don't feel like they're in a sausage skin and can occasionally pull their knees up. That's why we tailor our sleeping bags wider and even offer wide versions for people with broader stature. Because if your shoulders are snug in the sleeping bag, you'll experience a cold bridge due to the compressed insulation and less air insulation.
• Important: Contrary to popular belief, a tighter sleeping bag is not warmer. It warms up faster because there's less air inside to warm. But air also insulates, so looser models are more insulating. If you want more comfort (more room) with the right body size, you can of course go for the larger version. You'll just have to warm up more air.
• We've developed a  heating element for the sleeping bag . Since a sleeping bag doesn't heat itself, but only reflects body heat, you might find yourself exhausted and colder than usual after a long hike. The heating element can preheat the footwell for 10 minutes, and the sleeping bag retains the warmth throughout the night. This heating element is integrated into all Grüezi bag® DownWool-Hybrid mummy sleeping bags and can be retrofitted to the "Biopod DownWool-Hybrid Ice Alpine."
• We use high-quality RDS-certified down, which provides unique insulation. The  down to feather/support ratio is 90% down and 10% feather.  They also have a high fill power (at least 700 cuin+, and for the extra-warm DownWool hybrid sleeping bags, even goose down with at least 800 cuin+). 

Our tips and experience on the temperature range of sleeping bags