Confused by the numbers on a bag’s label? Sleeping bag temperature ratings come from a standardised lab test, and the comfort figures matter more than the extreme one.
Ratings are one piece of a bigger kit decision, so the camping guide covers the rest.
| Item | Value |
|---|---|
| Revised edition of the European sleeping bag standard | EN ISO 23537-1:2022 |
| 2016 edition of the standard | Withdrawal effective May 25, 2022 |
| Limit temperature for extreme climate conditions | -20 °C |
| Sleep period behind the lower comfort limit | Eight hours |
| Sleep period behind the extreme rating | Six hours |
| Heat a person generates while sleeping | 75/100 watts |
Figures come from the Genorma standards listing and Ferrino’s explanation of its temperature ratings. Standards get revised and makers change their methods, so check the sources before you rely on them.
What the standard behind the numbers covers
The rating on an adult bag traces back to the European standard EN ISO 23537-1, titled “Requirements for sleeping bags – Part 1: Thermal and dimensional requirements”. According to the Genorma listing, the 2016 edition was published on Dec 15, 2016 and followed EN 13537:2012.
As of that Genorma listing, the 2016 edition shows withdrawal effective May 25, 2022, and it is marked as revised by EN ISO 23537-1:2022. Ferrino’s page also cites EN ISO 23537-1:2022 for its own testing, so the 2022 edition is the one to look for when a maker names a standard.
The scope is narrower than many buyers assume:
- It covers adult-sized sleeping bags for sports and leisure time activities.
- It does not apply to military bags or bags for extreme climate zone expeditions.
- It does not apply to bags for children or babies, because no prediction model exists for them.
The standard’s own note puts the limit temperature for extreme climate conditions at -20 °C, according to Genorma. A bag built for colder trips than that sits outside the system entirely.
Comfort, lower limit and extreme: what each number means
Most labels show several temperatures, and they answer different questions. Ferrino defines them like this:
- Comfort temperature: the value, referring to a standard woman, that lets her sleep a full night in a relaxed position.
- Lower comfort limit: the minimum temperature, referred to a standard adult man, at which it is possible to sleep curled up for eight hours without waking (Ferrino).
- Extreme temperature: the minimum temperature at which the bag protects a standard adult from hypothermia, allowing six hours of uncomfortable sleep without dangerous drops in internal temperature (Ferrino).
The extreme figure describes a bad night that you survive, not a night you enjoy. Ferrino recommends that you take the comfort and intermediate temperatures into account when choosing, and to weigh them against your own level of athletic preparation.
How a bag gets its rating in the lab
Ferrino describes testing with a sensor-equipped mannequin that simulates the human body. The mannequin wears a two-piece suit of cotton or a cotton-polyester blend, with a thermal resistance between 0.040 and 0.060 m² K/W as specified by the ISO 11092 standard (Ferrino).
The bag lies on a foam mattress with a thermal resistance of Rct = 0.85, which rests on a 2 cm wooden slab that simulates an artificial floor with air passage. That setup means the mattress is part of the test, not an optional extra.
The standard describes assessing performance in steady-state conditions, which is a controlled model of a night, not a real one, as Genorma summarises it. It also notes that bags without homogeneous fillings, such as those with extra insulation in certain parts, pose issues with calibration and the test procedure.
Why the same bag feels different to different sleepers
A label gives you a standard adult, and you are probably not one. Ferrino lists the main body factors behind the feeling of hot and cold:
- Metabolism: while sleeping, a person generates 75/100 watts of heat, depending on age, sex, weight, habits and condition.
- Age: an older person generates less heat and feels cold earlier than a younger one.
- Gender: women generally feel the cold more than men, and Ferrino says the standard comfort value for women is 5°C higher than that for men.
- Habit: a lifestyle of heated homes and air-conditioned offices and cars reduces the body’s ability to tolerate cold.
- Experience and fitness: a beginner generally feels more discomfort, and exhaustion reduces heat production.
All of this comes from Ferrino’s guide. If you tend to sleep cold, pick a bag whose comfort figure sits well below the night-time lows you expect.
Making a rating work on the ground
The bag is only one layer of a sleep system. These habits, drawn from Ferrino’s tips, protect the warmth you paid for:
- Use a good mattress, which gives adequate insulation from the ground as well as comfort.
- Shelter from wind and damp, because direct wind and particularly humid conditions significantly increase heat loss through convection.
- Bring extra clothing that can be worn under your regular clothing at night.
- Eat and drink properly, and avoid alcohol, which gives only an initial sensation of warmth before you feel colder than before.
- Keep the bag dry, since wet sleeping bags, especially down ones, offer less insulation than dry ones.
Where you pitch matters for the wind point, so read how to pick a campsite before you settle on a spot. Warmth around the fire in the evening is a separate matter, and how to build a campfire safely covers that part.
Frequently asked questions
Which temperature on the label should I plan around?
Show answer
Ferrino recommends taking the comfort and intermediate temperatures into account. The extreme figure is the point where the bag only protects you from hypothermia, with uncomfortable sleep.
Do these ratings work for children’s bags?
Show answer
No. The standard does not apply to sleeping bags for children or babies, and its note says no prediction model exists for them, per the Genorma listing.
Has the standard changed?
Show answer
Yes. As of the Genorma listing, EN 13537:2012 was followed by the 2016 edition, which shows withdrawal effective May 25, 2022 and revision by EN ISO 23537-1:2022. Check which edition a maker cites.
Does a warmer rating mean I can skip a mattress?
Show answer
No. Ferrino advises a good mattress for ground insulation, and the lab test itself places the bag on a mattress.
