Temperature ratings
Temperature ratings were designed to give an idea of a sleeping bag’s performance. However, they became for many years an area subject to marketing abuse. Recent efforts have been made to resurrect their validity.
There is no international standard for measuring sleeping-bag performance. There are a number of national standards:
- UK
- British Standards BS4785
- USA
- ASTM F1720
- Europe
- EN13537
- Norway
- Thelma
- France
- NFG 08013
In 2005, the European standard EN 13537 became the official standard for the labelling of sleeping bags in the European Community. The standard is not mandatory, so brands are not legally required to comply (at the moment).
Most brands have, however, agreed to follow the EN13537 standard, although not necessarily to full compliance (which includes labelling information on fabrics and filling as well as temperature values). The minimum standard recommended by the European Outdoor Group (the outdoor trade organisation) is the labelling of temperature values as shown below:
- Upper limit
Highest temperature at which a standard adult male is deemed to have a comfortable night’s sleep without excessive sweating
- Comfort rating
Temperature at which a standard adult female can have a comfortable night’s sleep
- Lower limit
The lowest temperature at which a standard adult male is deemed able to have a comfortable night’s sleep
- Extreme
A survival rating only for a standard adult female. After 8 hours, hypothermia may start to start set in.
At crux, it is our opinion that the Upper Limit and Extreme figures are of not much value. Consequently, we quote the Comfort and Lower limits only. The EN13537 values are quite conservative, but we do feel they accurately reflect the temperature limitations of the sleeping bag for a comfortable night’s sleep. Obviously, individual tolerances may allow some people to go beyond these figures, but we believe this is at the discretion of the user and is not something to be claimed by us.
The EN13537 test uses a manikin that radiates heat. It is clothed with a simple base layer and placed in a sleeping bag in a chamber maintained at a constant temperature. The manikin is heated until it has reached a stable surface temperature of 34ºC (human skin temperature). The amount of energy required to maintain this surface temperature is then measured, and the thermal resistance (i.e. insulation) is calculated.
Naturally, the idea of the test is to duplicate real-use conditions. However, like all other similar tests, it fails on several counts. First, it relies on parameters for a “standard” male and female – which would be OK if these parameters were actually published and we could each measure our personal degree of deviation from “standard”. Second, our own “standard” condition varies from one day to the next depending on physiological and environmental conditions. Thirdly, the test gives temperature values at which the standard person will be comfortable – a concept that is impossible to quantify for any individual.
Another shortcoming of the EN13537 test lies in its use of a manikin. Bags that are smaller and fit the manikin more snugly will return better test results than a larger, more generously sized sleeping bag. So whilst the EN standard may attempt to create a “real-world” test of performance, the best it can achieve is a basis of comparison against competing products, and even then such comparisons can be distorted.
We are currently in the process of getting the Torpedo 500 tested by other recognized standards in an attempt to quantify the level of difference between the values of each respective norm.
