Since 2005 there has been a European standard, EN 13537, for measuring temperature limits on sleeping bags and all Fjällräven models are tested in accordance with this standard. This makes it easier to objectively compare sleeping bags. EN 13537 tests sleeping bags using a test dummy, and the temperature levels are set at four levels, with the middle levels being the most interesting from a user perspective.
Upper temperature limit – the temperature at which an average man can sleep without sweating too much. Measured with the hood and zippers open and the arms on the outside of the sleeping bag.
Comfort temperature – the temperature at which an average woman can sleep comfortably in a relaxed position.
Lower temperature limit – the temperature at which an average man can sleep eight hours without waking.
Extreme temperature limit – the lowest temperature at which an average woman can survive with the sleeping bag (although this makes no statement about the experience being comfortable).
Women should always look at the comfort temperature first while men should look at the lower temperature limit. Remember, though, that your experience is personal and affected by many other factors – read more under Perceived temperature.