Winter sleeping bags: how to read comfort and limit ratings

Many people who were cold in a sleeping bag last winter did not buy a bad bag. They read the number on it as the temperature at which they would sleep warm. That is not what the number means. Before you replace your bag, it helps to know what the ratings measure.

Comfort and limit: two different numbers

The current international standard for sleeping bag temperatures is ISO 23537-1:2022, which replaced the 2016 edition. It covers adult bags for leisure use with a limit temperature of −20 °C and warmer. A tested bag is labelled with more than one temperature, and the two that matter are these:

• Comfort: the temperature at which the average sleeper stays comfortable, in Kelty’s words. This is the figure to plan around.
• Limit (lower limit): a colder figure. Kelty’s help centre calls it the “lower limit or survival rating”. It is not a temperature at which you will sleep well.

The gap between them can be several degrees. Choose by the comfort figure, and treat the limit as the edge, not the target. Some people sleep colder than others, whatever the label says; if you know you feel the cold, give yourself more margin.

Kelty notes that it labels most women’s bags with the comfort figure and most unisex bags with the lower limit, and explains this by saying that women tend to get colder than men. So two bags with similar numbers on the label can be rated on different terms. Read which figure the number is.

What the number in a Kelty name means

Kelty puts a number in the name of most bags. It is the US label of the model, not degrees Celsius, and it is not a published comfort rating. A Cosmic Down 20 is labelled for about −7 °C. The Cosmic Synthetic 20 and the Supernova 20 carry the same label. Treat that figure as the cold end of the bag’s range, not as a temperature at which you will be comfortable. For reference, here is what the common Kelty names correspond to:

• A bag named 50: about 10 °C
• Named 40: about 4 °C
• Named 30: about −1 °C
• Named 20: about −7 °C
• Named 15: about −9 °C
• Named 0: about −18 °C

The three bags named 20 differ in fill and shape. The Cosmic Down uses trapezoidal baffles to hold the down in place. The Cosmic Synthetic is filled with CirroLoft ECO. The Supernova is down in a roomier shape for people who turn in their sleep.

Matching the rating to UAE nights

Some real numbers help. In early January 2025, Jebel Jais fell to 1.8 °C, and one visitor told The National her group had cut an earlier trip short because they were not prepared for the cold. In the dunes near Tal Moreeb, campers reported 9 °C at sunrise in December 2024. Khaleej Times advises packing sleeping bags rated for 5 to 10 °C for winter camping spots.

• Desert nights around 10 °C: a bag whose comfort figure is near 10 °C or lower.
• Desert nights near 5 °C or with a cold wind: a bag whose comfort figure, not limit, is at or below 5 °C.
• Mountains in January and February: plan for nights near freezing. A bag labelled for about −7 °C is not automatically enough; check its comfort figure if you can find it, and add a warm pad and a blanket.

Our guide on choosing a sleeping bag for winter in the UAE goes through each Kelty bag by trip type.

What moves you up or down the scale

A rating is measured in one fixed setup. On a real night, several things change how warm you are:

• The pad. The ground draws heat from you all night. Kelty explains that a pad with a higher R-value insulates you better from the cold ground. With a car, you can bring the Waypoint SI, the biggest and thickest pad in the Kelty range; for carrying, the self-inflating Mistral SI weighs under 1.4 kg in its stuff sack.
• Clothes. Dry base layers, socks and a hat. Clothes damp from the day make you cold.
• Food and water. A warm meal before bed helps; so does drinking enough during the day.
• The tent. It keeps off wind and dew. Do not count on it to add a set number of degrees.
• The bag’s age. Kelty notes that bags lose warmth over the years.
• You. Sensitivity to cold varies from person to person. If you usually feel the cold, choose by the comfort figure with a margin.

Before you buy a warmer bag

• Write down the coldest night you plan for: place and month.
• Find out which figure the label shows: comfort or limit.
• Check your pad first. Sometimes the pad is the problem, not the bag.
• Pick a bag whose comfort figure is at or below your coldest night, and bring a blanket for margin.