The EN13537 is a European standard for sleeping bags that provides three temperature levels to help guide you when choosing a bag.
COMFORT (Comfort Temperature): Measured under a standard test environment for standard healthy women in a relaxed state, they will not feel cold (shaking all over), and they will keep their body comfortable throughout the night.
LIMIT (Limited Temperature): Measured under a standard test environment for a standard healthy man curled up in a sleeping bag, his body did not tremble, and he could keep his body comfortable throughout the night.
EXTREME (Extreme Temperature): Measured under a standard test environment for standard healthy women, who are attacked by severe cold weather (shaking all over). At this time, there is a threat of hypothermia or even death. The limit temperature belongs to the theoretical range and is only regarded as a dangerous critical point that is difficult to reach.