Understanding Sleeping Bag Temperature Ratings

Have you ever gone camping and been cold, or have you decided not to go camping because it was too cold? Well, if you understood sleeping bag temperature ratings, then you might not experience these issues. Sleeping bag temperature ratings can get fairly complicated, however. Luckily for you, in this article, we are going to look at sleeping bag temperature ratings and break them down. We are going to focus on what a sleeping bag temperature rating actually means, and help you understand them. This way if you go camping in cold weather you shouldn’t get cold again. Read on to learn all you need to know about what sleeping bag temperature ratings are and how to understand them.

Understanding Sleeping Bag Temperature Ratings

Understanding Sleeping Bag Temperature Ratings

What is Sleeping Bag Temperature Ratings ?

So first, what is a sleeping bag temperature rating? Well, it is a rating that says a sleeping bag should keep you comfortable up to a set temperature. The first thing to remember though is that sleeping bag temperature ratings are generally given in ranges and each part of the range has different meanings. Most bags will have a bar that gives you the range. You have the T-comfort zone and the T-limit zone. Along with this you typically have the words comfort, transition, and risk along the bar with the different numbers. Before getting into what all these different things mean though, on the temperature rating, we are first going to look at how temperature ratings are determined.

Determining Temperature Rating

Determining Temperature Rating

Determining Temperature Rating

So, in the early days of sleeping bags, some companies put temperature ratings, but there was no set method of determining them. This means that you could not compare bags from one company to the next. This changed when the industry decided to have an independent lab do the testing. When an outside lab started doing the testing this brought about the EN or ISO ratings which you see on bags today. Today the testing is all standardized and is an exact science.

The way sleeping bags are tested for temperature today is that a dummy with a lot of sensors is put into the bag. The bag is then put into a room where the temperature can be controlled. They drop the temperature of the room slowly and pay attention to the mannequins sensor readouts. They pay attention to when certain areas reach certain temperatures and mark it down.

Then, after the experiment, they compile the data and assigned the bag a temperature rating on the scale. This is a simplified explanation, but it is a good enough one for you to understand temperature ratings of sleeping bags. Normally multiple of the same bag is tested at once to check for quality control of the bag and get an accurate average. However, one thing to remember is that labs can simulate real-world experiences, so the temperature rating that is assigned should just be used as a guide.


So, now we can start talking about the scale and the different zones and different numbers. First, we have the comfort rating which is always the larger number. This is the number that a cold sleeper can stay warm or comfortable in the bag. It is the number used on women’s bags. Then you have the lower limit rating. This is less than the comfort rating and it is the temperature that a warm sleeper can stay comfortable in the bag. It is the number used on men’s bags.

So, now that you know what the numbers mean, what do the ranges mean? Well, the comfort range is the temperature at or above where a “standard” women feel comfortable and are able to sleep in a normal relaxed position. This means they don’t have to bundle up in a ball. The transition range is the area of temperature where a “standard” man is bundled up in a ball and at thermal equilibrium. This means they aren’t shivering and with the bags help they aren’t losing heat, but they are having to hold all their own heat in. The transition range is the limit of the bag for safe sleeping. Below that you get the risk range. Another name for this range is the extreme range. In the extreme range, the sleeper is under extreme cold. They are shivering and at risk of hypothermia. A bag should only be used in this range in an emergency.

Temperature Range Aren’t Rules

One key thing to remember though is temperature ranges aren’t rules. They just range base on a lab test. Labs, however, can not factor in real-world things. For example, they don’t know how much everyone that is going to be using the bag weights. If you are heavier or have more meat on your bones, then you will put off more heat. Also, sleeping bag testers can’t test what you are going to be wearing. If you are wearing warm clothes, then you will stay warm in cooler temperatures faster then if you aren’t dressed warmly. Your tents insulation also plays a big role in how effective your sleeping bag is. Lastly, your sleeping bag fit is important. You want one that is snug, but not too restricting. This will help hold in most of your body heat.


Understanding sleeping bag ratings can be complicated. This is especially true if you are looking at older bags that don’t have ISO numbers or EN numbers. If the rating is not one of those, then it is pretty much useless because it wasn’t formed with the standard test. However, now you know how to understand ISO numbers and EN numbers. You also know what each range means. You know that the comfort rating is the lowest temperature a cold sleeper can stay comfortable and sleep in a normal position. You also, know that the lower limit number is the coldest it can be for a warm sleeper to sleep in a ball position and stay warm. Lastly, though you know that temperature ratings are just a guide and not rules. They don’t factor in everything about each individual such as is and what they are wearing. Now, that you know how to understand sleeping bag temperature ratings though you should be able to camp in cool weather and not get cold.

Tom Chandler

"When your hands hit the floor, they get cut up. When mine hit the floor, they slide with ease"

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