Selecting the right sleeping bag for hiking/camping use is one of the most important equipment choices you will make. If you go too hot then you can always unzip the bag or use as it as a quilt. If you choose an inadequate sleeping bag you will have either a cold nights sleep at best, or it could lead to hypothermia or worse.
In an attempt to provide an industry standard a sleeping bag bag standard was developed and over the year this has been updated with the current standard now being ISO 23537-1:2022. This standard is probably the only accurate way of comparing one sleeping bag to one another in any meaningful way. ISO 23537-1:2022 standard provides three main temperature levels to guide a consumer in their choice:
Upper Limit – The temperature at which a standard man can sleep without excessive perspiration. It is established with the hood and zippers open and with the arms outside of the bag.This rating is typically not used on commercially available sleeping bags.
Comfort – The temperature at which a standard woman can expect to sleep comfortably in a relaxed position. If you are a male you will find that the bag in question will be comfortable to a lower temperature than the comfort rating.
Lower Limit – The temperature at which a standard man can sleep for eight hours in a curled position without waking. If you consider yourself a warm sleeper you can use this rating to decide the coldest temperature the sleeping bag is suitable for.
Extreme – This is a survival only rating for a standard woman. Between the lower limit and the extreme rating a strong sensation of cold has to be expected and there is a risk of health damage due to hypothermia. This is an extreme survival rating only.
The EN13537 temperature tests use a thermal manikin with heaters and temperature sensors to measure the insulation value of a sleeping bag. For the purpose of these measurements, a “standard man” is assumed to be 25 years old, with a height of 1.73 m and a weight of 73 kg; a “standard woman” is assumed to be 25 years old, with a height of 1.60 m and a weight of 60 kg. The manikin is wearing one layer of long underwear and is placed inside the sleeping bag on an insulating mat. The test is conducted in a temperature controlled chamber and a range of comfort temperatures are derived from measuring the energy required to maintain homeostasis in the manikin to a set temperature.
A temperature rationing scale based on the EN13537