All of our sleeping bags have been tested to the EN13537 standardized test to determine their temperature rating. These ratings are based on the user wearing a layer of long underwear and a hat and using an insulated sleeping pad. For the women’s specific sleeping bags in our line, the rating is based on the average female having a comfortable night’s sleep, which is called the T-comfort rating. The rating based on the average male having a comfortable night’s sleep is called the T-limit and is generally much lower for the same item. Women generally lower their body temperatures slightly more than men over the course of the night, necessitating a slight increase in the amount of insulation used.