The EN (European Standard) rating is a rigorous test designed to set measurable goals and standardize the marketing of sleeping bags. It is designed to help consumers make an informed decision by using independently derived temperature ratings.
Each EN sleeping bag test results in four temperature ratings - upper limit, comfort, lower limit and extreme, with the following definitions:
From Wikipedia:
Upper limit - the temperature at which a normal man* can sleep without excessive perspiration. It is made with the hood and zippers open and with the arms outside the pocket.
Comfort - the temperature at which a normal woman* can expect to sleep comfortably in a relaxed position.
Lower limit - the temperature at which a normal man can sleep in a curled position for eight hours without waking up.
Extreme - the minimum temperature at which a normal woman can stay for six hours without risk of death from hypothermia (although frostbite is still possible).
For the purpose of these measurements, it is assumed that a "normal man" is 25 years old, 1.73 m tall, and 73 kg; a "normal woman" is 25 years old, 1.60 m tall, and 60 kg.
The three most common ratings are comfort, (lower) limit, and extreme. For men's bags, most companies advertise the Limit rating, and for women's bags, the Comfort rating, although it can vary."
