The EN Rating scale is a scientific test to determine the warmth of a sleeping bag. The test produces a Lower rating (for male sleepers) and a Comfort rating (for female sleepers). Both are listed in the features table on the product page.

A unisex sleeping bag with a Lower limit of -10°C means a man should be comfortable down to air temperatures of -10°C. The same bag will also have a Comfort limit, in the realm of -3°C, so a woman would be comfortable down to an air temperature of -3°C. These ratings require a sleeping mat with an R-Value appropriate for expected ground temperatures – without this, the sleeping bag itself is unlikely to keep the sleeper warm enough.

A variety of factors impact sleeping bag warmth - the above temperatures are merely guidelines, not guarantees. It’s important to think of a sleeping bag, an appropriately insulating sleeping pad and a liner as a sleep system. For example - if you plan on sleeping in nighttime air temperatures of -3°C, choose a bag with a gender-appropriate rating of -5°C, plus a sleeping mat with an R-Value of 2.5 to 3, and consider a Reactor thermal liner.