Your guide to sleeping bag temperature ratings

As a team that is passionate about outdoor life, we understand what makes superlative outdoor equipment no matter the camping style or chosen adventure.  We also know that no matter how good our materials or the designs we create, it is hard to make an informed choice when purchasing without a way to compare performance.

Well, we want to make sure you can purchase one of our sleeping bags in confidence and that’s why we test our adult sleeping bags to EN ISO 23537-1. 

This is your reliable guide to a sleeping bag’s performance. No matter the brand or model, if a sleeping bag complies to the latest official European Standard it has been subjected to officially recognised industry tests to obtain an accurate temperature rating. 

It is an expensive and resource-intensive process. To obtain a Standard rating for each model, we send a sample sleeping bag to an official independent test facility. Here, a computer-controlled thermal mannequin is used to determine the sleeping bag’s temperature limits. The heated mannequin, which is standard adult size, is placed inside the sample sleeping bag in a temperature- controlled climate chamber. Tests are carried out to obtain specific measurements that include heat build-up, sustained temperatures, temperature loss and rate of loss. The results create the recommended temperature limits that appear for each of our sleeping bag models.

The results are displayed as three measurements in degrees Centigrade. And our standard format in which we present the rating ensures an easily understood like-for-like comparative performance rating to help you choose the appropriate sleeping bag for your needs. These measurements are:

Tcomfort – This is the lower limit that a ‘standard’ woman can sleep comfortably in a relaxed position, such as sleeping on their back. We consider this and above the optimum temperature range for everyone’s sleep comfort over time but, given the gender specific character of this measurement, we use the female symbol when space prohibits the use of ‘Tcomfort’ – such as sleeping bag labels.

Tlimit – This is the lower limit that a ‘standard’ man can sleep in comfort in a curled position to preserve body heat and resist shivering. It is close to the limit of a sleeping bag’s performance and if you aim to sleep within this range for extended periods it is wise to invest in a different model or a liner that will boost insulation and comfort levels. Given the gender specific character of this measurement, we use the male symbol when space prohibits the use of ‘Tlimit’ – such as sleeping bag labels.

Textreme – This is the lowest temperature that you can expect to survive a night in a sleeping bag. As the rating name suggests and given the risk of hypothermia, this is an extreme case scenario and should only be considered if you might potentially experience such temperatures in an emergency.  
It is important to recognise that these are ‘standard’ temperature ranges and performance will be influenced by other factors that include and are not restricted to, shelter, body type and physical conditioning, food taken and hydration, climatic conditions, mat insulation (often defined by a comparative-performance R-value that, like sleeping bag ratings, is the result of independent testing), clothes worn, external heat sources like hot water bottles… The list goes on but at least the EN rating is a handy baseline tool to work with when choosing a sleeping bag…