Gina Johnson
Sleeping bags come in a variety of temperature ratings, which indicate the range of temperatures for which a sleeping bag is suitable. The temperature rating of a sleeping bag is a key factor when choosing one. The current ISO 23537 sleeping bag test standard, which uses a heated mannequin with multiple temperature sensors, is recognised globally. However, real-world comfort may differ from the tested temperature rating due to variations in people's clothing, gear, body types, weather conditions, and other factors. Sleeping bags with lower temperature ratings tend to have a snugger fit and may require additional layers for comfort. It is recommended to choose a sleeping bag with a lower temperature rating than the lowest expected nighttime temperature at your camping location.
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What You'll Learn
Sleeping bag temperature ratings
There are three main temperature rating categories: the EN (European Norm) or ISO standard, trustworthy homebrew ratings (usually from cottage companies), and ratings from untrustworthy companies who may cheat the system. The EN/ISO standard includes the Upper Limit, Comfort, and Lower Limit ratings. The Upper Limit rating is the temperature at which a standard male can sleep without excessive perspiration, with the hood and zippers open, and arms outside the bag. The Comfort rating indicates the temperature at which a standard female can sleep comfortably through the night without curling up for warmth. This is the rating used for women's bags. The Lower Limit rating is the temperature at which a standard man can sleep for eight hours in a curled position without waking. This is the rating used for men's bags.
It's important to note that temperature ratings are estimates and not exact guarantees. Individual factors such as body type, clothing, and sleeping pads can affect the comfort level of a sleeping bag. Additionally, the numbers on bag names may not always match the exact temperature ratings, so it's essential to check the specific ratings provided by the manufacturer. When choosing a sleeping bag, it's recommended to consider the coldest conditions you anticipate and select a bag that will keep you warm at or below that temperature. It's also a good idea to prepare for unexpected temperature drops by bringing a bag rated slightly lower than the expected lowest temperature.
Some additional factors to consider when choosing a sleeping bag include its weight and warmth-to-weight ratio, especially if you're backpacking and need a lightweight and easily packable option. You might also want to think about combining multiple bags for different seasons or using a liner to adjust the temperature rating of your bag. Checking the R-value of the sleeping pad and ensuring it matches the expected ground temperatures is crucial, as a suitable sleeping pad can significantly impact the overall warmth of your sleep system.
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How to choose a sleeping bag
When choosing a sleeping bag, the key factor to consider is its temperature rating. This is because the temperature rating identifies the lowest temperature at which a bag is designed to keep a sleeper warm. Here are some tips on how to choose a sleeping bag based on temperature:
Understand the temperature ratings
Sleeping bags have different temperature ratings, such as the "comfort" rating, the "lower limit" rating, and the "extreme" rating. The comfort rating indicates the temperature at which a colder sleeper will be comfortable, while the lower limit rating is the lowest temperature an average sleeper would be comfortable in. The extreme rating is a survival rating, indicating the temperature at which the bag will keep you from freezing.
Consider the seasonality
Sleeping bags are often rated by seasonality, with one-season bags designed for summer use, two-season bags for spring and summer, three-season bags for spring, summer, and autumn, and four-season bags for winter use. If you're planning on camping in colder months, choose a bag with a lower temperature rating than the lowest anticipated temperature.
Look for standardised tests
To ensure accurate comparisons between different brands, look for sleeping bags with EN or ISO temperature ratings. These standardised tests use a heated mannequin with temperature sensors to determine the bag's temperature rating. The EN rating scale, for example, provides a Lower rating for male sleepers and a Comfort rating for female sleepers.
Choose the right insulation
The type of insulation is an important consideration. Down insulation is lighter, more compressible, and more durable than synthetic insulation, but it is also more expensive and less suitable for rainy conditions. Synthetic insulation, on the other hand, stays warm when wet and is more ethical and affordable, but it is heavier.
Additional considerations
Other features to look for include a snug-fitting hood for added warmth, multiple zipper sliders for ventilation, and a stash pocket for small items. A sleeping bag liner can also add extra warmth and help keep your bag clean. Finally, consider the size and shape of the bag, ensuring you have ample room to stretch out and roll over.
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Seasonality
The temperature rating of a sleeping bag is a key factor when choosing one. Sleeping bags are designed for different seasons, with temperature ratings corresponding to the four seasons of spring, summer, autumn, and winter, or a combination of these.
A one-season sleeping bag is designed for summer camping and backpacking, where night-time temperatures will stay above +5° Celsius/Centigrade (C) or approximately 40° Fahrenheit (F). Two-season sleeping bags are designed for slightly cooler nights in spring and summer, with a temperature range of 0 to +5°C (or approximately +30 to +40°F). They are also suitable for milder autumn nights or for people who sleep cold even in summer.
Three-season sleeping bags are designed for colder nights throughout spring, summer, and autumn, when overnight temperatures might dip just below freezing (down to -5°C or approximately 20°F). They offer a good balance between warmth, weight, and bulk, making them versatile and popular for a range of camping and backpacking trips.
Four-season sleeping bags are designed for winter use, with temperatures dropping to around +15°F or -10°C. The term five-season is sometimes used to indicate a sleeping bag for expedition or high-altitude use, suitable for extremely cold temperatures ranging from -10°C to -40°C.
It is important to note that the temperature ratings are based on an "average sleeper" and may not account for individual variations in clothing, gear, body type, metabolism, and other factors. When choosing a sleeping bag, it is recommended to pick one with a lower temperature rating than the lowest expected nighttime temperature at your camping location. Additionally, factors such as the shape, size, and features of the sleeping bag can also impact its warmth and comfort.
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Lab testing
The test is conducted in a controlled environment, typically a third-party laboratory, to ensure consistency and objectivity. A heated thermal mannequin, fitted with temperature sensors, is dressed in standardised base layers, including a baselayer top, tights, long socks, and a hat. The mannequin is then placed inside the sleeping bag, which is positioned on a closed-cell foam sleeping mat or an insulated sleeping pad with a minimum R-value of 4.
As the ambient temperature in the chamber drops, measurements are taken at multiple points on the mannequin's surface to determine the amount of energy required to maintain a standard skin temperature. These measurements are compared to reference sleeping bags to calculate three primary ratings: Comfort Rating, Lower Rating, and Extreme Rating.
The Comfort Rating indicates the temperature at which a standard woman could sleep comfortably for eight hours. It is typically used as the temperature rating for women's sleeping bags. The Lower Rating, which is always lower than the Comfort Rating, represents the temperature at which a standard man could sleep comfortably for eight hours. This rating is used for men's sleeping bags. The Extreme Rating is a 'survival' rating, indicating the minimum temperature a person could remain in the sleeping bag for a limited time without ruling out frostbite.
It is important to note that lab testing has some limitations. The mannequin remains stationary during the test, which means it does not account for real-world factors such as body movement, changing weather conditions, or variations in individuals' clothing, gear, body types, and food intake. Therefore, the lab-tested temperature ratings may not perfectly match real-world comfort levels.
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Real-world comfort
Sleeping bag temperature ratings are based on an "average sleeper" and are useful for comparing bags. However, real-world comfort may differ from the tested temperature rating due to various factors. Firstly, the temperature ratings are determined through standardised tests such as EN 13537 and ISO 23537, which use a heated mannequin with temperature sensors to simulate a sleeping person. These tests provide a more precise comparison than season ratings, which indicate the time of year a bag is suitable for. For example, a one-season bag is designed for summer use, while a three-season bag can be used throughout spring, summer, and autumn. However, real-world conditions can vary from the controlled test environment, impacting the bag's comfort level.
The comfort rating of a sleeping bag is influenced by individual factors such as body type, clothing, gear, metabolism, and sleeping patterns. For instance, some people may be naturally warmer or colder sleepers, affecting their comfort level. Additionally, the clothing and gear one uses, such as sleeping pads and liners, can alter the bag's effectiveness in maintaining warmth. It is worth noting that the EN and ISO ratings are voluntary, and not all sleeping bags have these ratings. In such cases, the temperature rating may reflect the brand's estimate rather than standardised test results.
The shape and features of a sleeping bag also contribute to its real-world comfort. Sleeping bags come in various shapes, including rectangular, semi-rectangular or "modified mummy", and mummy. Rectangular bags offer more room to stretch out, while mummy bags are snug-fitting to boost warmth and reduce weight. Features such as hoods, multiple zippers, and stash pockets can also enhance comfort and convenience.
When choosing a sleeping bag, it is essential to consider your specific needs and preferences. For example, if you tend to sleep cold, you may need a bag with a higher temperature rating or additional insulation. Additionally, factors such as cost, pack size, and fill material should also be considered. It is recommended to try out different bags to determine which styles and features suit your comfort and functionality requirements.
Lastly, it is worth noting that the temperature rating of a sleeping bag is typically a survival rating rather than a comfort rating. In other words, it indicates the minimum temperature at which you can survive rather than sleep comfortably. Therefore, it is generally advisable to select a bag with a lower temperature rating than the expected nighttime temperatures and consider additional insulation if necessary.
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Frequently asked questions
The temperature of your sleeping bag depends on the season and location of your camping trip. Sleeping bags are available in one, two, three, four, and five-season ratings. One-season bags are designed for summer use, while three-season bags are suitable for spring, summer, and autumn. Four-season bags are designed for winter use, and five-season bags are for high-altitude expeditions.
Temperature ratings for sleeping bags are determined by standardised tests, such as EN 13537 and ISO 23537. These tests use heated mannequins with temperature sensors to determine the sleeping bag's thermal resistance. The tests produce three temperature ratings: the lower limit for male sleepers, the comfort rating for female sleepers, and the extreme temperature where there is a risk of hypothermia.
When choosing a sleeping bag, consider the lowest nighttime temperature you expect at your camping location. It is recommended to pick a bag with a lower temperature rating than the lowest expected temperature. Additionally, consider your personal preferences, such as whether you tend to sleep warm or cold, and your budget, as warmer bags tend to be more expensive.
