The EN13537 is a European standard for sleeping bags that provides three temperature levels to help guide you when choosing a bag.
Comfort The temperature at which a standard woman can expect to sleep comfortably in a relaxed position. If you are female or consider yourself a cold sleeper, use this rating to decide the coldest temperature the sleeping bag is suitable for. We emphasise the Comfort temperature for our women’s specific sleeping bags.
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, use this rating to decide the coldest temperature the sleeping bag is suitable for. We emphasise the Lower Limit temperature for all our unisex sleeping bags.
Extreme This is a survival only rating for a standard woman. Between the lower limit and the extreme rating a strong sensation of cold must be expected and there is a risk of health damage due to hypothermia. This is an extreme survival rating only; we do not recommend you rely on this rating for normal use.