Lower limit rating

Lower limit rating is the second figure from the EN 13537/ISO 23537 sleeping bag standard, describing the point at which a standard warm sleeper, modeled as less cold-sensitive than the comfort rating's test subject, can stay warm for eight hours in a curled, defensive position rather than lying flat and relaxed.

It sits between the comfort rating and the extreme rating, and it exists because sleepers vary in how much cold they tolerate before waking or shivering. A bag rated to this number on a cold night will likely keep you asleep, but curled up and slightly cold rather than genuinely comfortable, which matters when you want to feel rested the next morning.

Use the lower limit as a rough floor for occasional cold nights, not a target for regular use, and check whether it or the comfort rating is the headline number on a listing, since retailers sometimes lead with whichever figure looks warmest. Pairing a bag near its lower limit with a higher R-value pad helps close the gap between the lab test and a real vehicle floor.