How To Determine A Sleeping Bag’s Rating


A sleeping bag is designed to keep you warm while enjoying the great outdoors.  The most comfortable bags, will keep your body heat where it belongs-inside your bag, in a variety of temperatures.  For this article, I’m going to explain how to determine a sleeping bag’s rating.

Determining a sleeping bag’s rating is fairly easy to accomplish. Most sleeping bags will specifically state right on the price tag or inside the bag, the ideal temperature for use.  These are general guidelines.  A sleeping bag rated for summer temperatures may be too cold for someone who is chilly all the time. A winter rated bag may be too warm for a hiker who sleeps hot.  The best bag for you will be based on when and where you are camping and your metabolism.

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Sleeping Bag Ratings

When you camp, you want a sleeping bag that is comfortable and warm.  Even when you are camping in 65-degree weather, you need a sleeping bag to keep the midnight breeze off the mountains from stealing your body heat.  Sleeping bags are your protection from chilly nights, brisk mornings and all those insects.  No matter what time of year you are camping, you will need to stay warm.

To make shopping for a bag easy, the sleeping bag industry created a rating system.  In general, there are three ratings: summer, three-season and winter.  Summer rated bags are designed with enough insulation to keep you warm in temperatures above 35 degrees. Three-season rated bags are tough enough for temperatures ranging from 10 degrees to 35 degrees.  Winter rated sleeping bags will keep you warm when the mercury drops below 10 degrees.

These ratings are general guidelines.  What works for one person, may not work for another hiker.  The sleeping bag rating is to be used as a starting point.  How hot or cold you sleep at night, where you are camping, the weather, what you are wearing, the quality of your tent all make a difference in how warm your sleeping bag will be.

Determining Temperature Rating

Thermometer
Thermometer

So, how do you really know that winter rated bag will keep you warm when the temperature drops below freezing on your next alpine expedition? You certainly don’t want to wait until you’re on the side of the mountain to figure out that fancy down bag isn’t working at all. In the past decade or so, consumers have demanded a more universal testing method to determine temperature rating for sleeping bags.  Before, it was up to each manufacturer to set temperature ratings. These ratings often varied from brand to brand, making it even more confusing for a consumer.

For example, a summer rated bag for one company may be a three-season bag for another company. After a lot of confusion, Europe stepped in and created testing standards for sleeping bags. This is referred to as EN 13537.  These standards make it easy to compare sleeping bag ratings from one company to the next. Even though this is a European based regulation, the standards landed across the pond when REI began requiring all the brands it carries to implement these testing procedures.

The EN 13537 testing methods involve placing a mannequin with sensors inside a sleeping bag. The temperature around the experiment is then dropped and researchers make note when the sleeping bags begins to lose heat and where it’s losing heat. This experiment makes it possible for manufacturers to determine four different ratings: upper limit, comfort, lower limit, extreme.

The upper limit rating is the temperature someone can sleep without sweating.  The comfort rating is the temperature you can sleep most comfortable, without adding extra layers.  The lower limit is the temperature at which someone sleep in a sleeping bag for six hours without getting cold.  The extreme limit is the lowest temperature someone can sleep inside the bag without suffering hypothermia. However, according to the EN 13537, the extreme rating doesn’t protect you from frostbite.

You’ll notice most sleeping bag companies will list all the ratings to make it easier for you to understand the capabilities of the sleeping bag. Let’s take a look at the Marmot Angel Fire Sleeping Bag designed specifically for women. This sleeping bag is rated for 25 degrees. So, technically this is a three-season sleeping bag. Online REI lists in detail the EN lower limit and the EN comfort limit. The lower limit is listed at 9.1 degrees. This means even though this bag is rated for 25 degrees, you won’t die if the mercury reaches 9.1 degrees.  The EN comfort limit on this bag is listed at 21.6 degrees. This means you will be most comfortable- not too hot or too cold when it’s exactly 21.6 degrees outside.

You can find the EN rating system on the manufacturer website of a sleeping bag you are interested in or it’s often printed on the label inside the bag.  Knowing the limitations of the bag, is important when you are camping in the great outdoors. The temperatures can change drastically throughout the day, especially if you are hiking at a higher elevation.  Knowing the capabilities of your sleeping bag could very well save your life if you ran into a cold weather snap.

When researching sleeping bags, it can be exceptionally helpful to have these included temperature ratings.  You want to know how cold the temperature can drop before you have to start worrying about frostbite and hypothermia. While having an industry standard temperature rating system is helpful, it’s still just a guideline. As I mentioned earlier, there are several other factors that will determine how warm that sleeping bag will actually be.

Your Metabolism And The Rating

Metabolism
Metabolism

The rating of a sleeping bag is only one part of the puzzle in determining how warm or cold the bag will feel for you. Your body’s metabolism plays a role in how hot or cold you sleep at night.  Do you need just a thin layer of blankets, even when it’s chilly? Do you wake up in a sweat every night, no matter how many or how little covers you are wrapped in? If this sounds like you, chances are you are a hot sleeper.  Keep this in mind when shopping for a sleeping bag. If you are always warm, a three-season sleeping bag might cut it in sub-zero temperatures.

If you tend to always be chilly, cold hands and cold feet no matter what you do, you may need a sleeping bag rated warmer for the actual conditions. Women tend to run colder than men and that’s why some brands have developed sleeping bags specifically for women. The bags tend to fit a women’s body better and provide better insulation in the feet and upper body area- where you are most prone to getting chilled. When in doubt, choose a sleeping bag that is warmer than what you may actually need. It’s easier to cool off then it is to warm up inside a sleeping bag.

Sleeping Pad/Liner

Sleeping Pad
Sleeping Pad

Even with a warm sleeping bag, if you are sleeping directly on the cold ground you could lose a lot of body heat. This known as conduction.  Conduction occurs when you transfer heat to a colder object or surface.  For example, if you walk around barefoot on the ice-cold ground, the heat from your feet is transferred to the cold ground. You lose body heat and suddenly you are struggling to stay warm. The same thing happens when you are camping in cold weather. However, a sleeping pad can prevent the transfer of heat and keep you more comfortable throughout the night.

Advances in technology, mean you have more options when it comes to sleeping pads.  Long gone are the days of thick foam pads.  Those work well in cabins or car camping, but you don’t want to be hauling a foam pad up the side of a mountain. Most camping sleeping pads are lightweight, easy to pack and are self-inflating. Just unroll the sleeping pad and it will naturally fill with air.

These soft air pockets mimic the comfort of a mattress. Yes, they are that comfortable.  A sleeping pad will keep you off the ground and away from the cold.  Adding a sleeping pad to your sleeping bag will keep you warmer and more comfortable no matter what Mother Nature throws your way.

A bag liner is another way to add warmth to your sleeping bag. Let’s say you have a summer rated bag and suddenly there’s a cold snap while you are on a three-day adventure in the Rocky Mountains. Liners fit snug inside your sleeping bag to give you extra warmth and comfort. Lines are available in a variety of materials to match your needs: thermal liners, microfiber and silk liners, fleece liners and even liners with a insect shield.  If it gets too hot to be inside your sleeping bag, you could always use a liner alone outside the bag to be comfortable, but not have the added weight of a sleeping bag. Liners are affordable to with most retailing for $25-$50.

Summer Rated Bag

Summer Rated Sleeping Bag
Summer Camping

As I mentioned earlier, a summer rated bag is perfect for when the temperature is above 35 degrees. Summer bags tend to be the most basic of sleeping bags.  Because they are rated for warmer temperatures they don’t have all the bells and whistles you will find in a winter bag.  You’ll find summer bags are also budget friendly.  You can find a great summer rated sleeping bag for under a hundred dollars.

While it’s important to stay warm while camping in the summer months, a summer rated bag is really all about comfort.  Summer rated bags are typically synthetic insulated.  Synthetic insulation is warm, cozy and can hold up to wet weather. Down is typically reserved for three-season and winter rated bags. Synthetic bags tend to be a bit bulkier than down, but if you are camping in your backyard or car camping you won’t mind the extra weight. In fact, you might find it incredibly cozy.

Three-Season Sleeping Bag

Wet Weather Camping
3 Season Camping

A three-season bag is a great choice if you don’t want to buy a new sleeping bag for every month of the year. If you live in a region where there are four distinct seasons, this type of sleeping bag will keep you warm and comfortable for most of the year.  Three-season sleeping bags are rated for temperatures ranging from 10 to 35 degrees. That’s cold! You’ll find three-season bags to be a bit more of an investment. Because this bag needs to keep you warm in freezing temperatures, it needs more insulation and a few extras to keep the warm air in and the cold air from getting inside.

You’ll find three-season bags with synthetic insulation and down insulation.  Down tends to keep you warmer in extreme cold. However, down is only effective when its dry.  Look for a down sleeping bag treated with a water-resistant coating to keep the moisture away. Three-season bags tend to be more expensive than summer bags, with prices ranging from $100-$400.

 Winter Sleeping Bag

Winter Rated Sleeping Bag
Winter Camping

A winter rated bag is made for the most extreme weather on the planet.  Winter bags are designed to keep you cold in weather below 10 degrees. You’ll find many bags in this category that will actually keep you warm in -25 degrees or colder. To keep you warm in extreme cold weather, winter bags are packed with a high down fill count. In general, the higher the fill count, the warmer the bag.  A winter rated bag will most likely have at least an 800-down fill count.

Winter bags also have hoods, draft tube and special anti-snag zippers to keep you warm all night long.  Winter bags are typically mummy shaped to keep the warm air and insulation close to your body.  Mummy bags work the best in cold weather! Winter bags are the most expensive out of the three sleeping bag ratings, with prices ranging from $500 to $1,200. Winter bags are an investment, but well worth the money when you are camping in extreme cold.

See also “When To Use A Sleeping Bag Liner“.

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