Colin Snow
Sleeping bag temperature ratings are based on standardised tests, such as the ISO 23537 test, which is recognised globally. The test involves placing a heated manikin with multiple temperature sensors inside a sleeping bag in a climate-controlled room on a standardised mat. The manikin measures the power needed to maintain warmth in a cold room, determining the sleeping bag's thermal resistance. This standard produces three temperature ratings: a comfort rating, a limit rating, and an extreme rating. However, it's important to note that these ratings are estimates, and real-world comfort may differ due to various factors such as individual preference, metabolism, and age, clothing, gear, body type, weather conditions, and food intake. When choosing a sleeping bag, it's crucial to consider your own personal internal thermostat and the expected coldest conditions during your adventure.
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What You'll Learn
Sleeping bag ratings are estimates
The standardized testing used to assign temperature ratings to sleeping bags provides three temperature thresholds: a comfort rating, a limit rating, and an extreme rating. The comfort rating indicates the temperature at which a cold sleeper might feel comfortable, and it is typically used for women's bags. The limit rating is the temperature at which a warm sleeper might still feel comfortable, and it is used for men's bags. The extreme rating indicates how cold the air could be before there is a serious risk of hypothermia or death.
It is important to note that not all sleeping bags have an ISO or EN rating. The test standard is not valid for bags designed for extreme cold or children's bags. In these cases, the temperature rating is likely the brand's estimate and should be used as a rough guideline rather than an absolute comparison to similar bags from other brands.
To choose the right sleeping bag, it is essential to consider various factors besides the temperature rating. These factors include the fit of the bag, the warmth of the sleeping mat, personal preferences, metabolism, age, and individual differences in body temperature regulation. Additionally, it is crucial to check the weather conditions and prepare accordingly before spending a night outdoors.
Sleeping bag ratings are essential in helping consumers choose the right bag for their needs. However, it is important to remember that they are estimates and should be used as a guide, along with other factors, to make an informed purchase decision.
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Lab testing methods
The EN and ISO tests are the standardised testing methods used to assign temperature ratings to sleeping bags. These tests involve placing a heated mannequin fitted with 15 temperature sensors to represent a sleeping person. The mannequin is dressed in a baselayer top, tights, long socks, and a hat, then placed inside the sleeping bag on top of a closed-cell foam sleeping mat, inside a cold chamber. The temperature of the air is then cooled, and the amount of electrical energy needed to maintain the mannequin’s initial temperature is measured. If it takes a lot of energy input to keep the mannequin warm, then the bag isn’t very warm.
The ISO test provides three temperature thresholds: a comfort rating, a limit rating, and an extreme rating. The comfort rating is based on the air temperature at which the "average female" can sleep comfortably through the night. The limit rating is based on the temperature at which the "average man" can maintain his thermal equilibrium in a curled-up position. He won't necessarily be comfortable, but he can sleep without shivering and is not in danger of hypothermia. The extreme rating gives an idea of how cold the air could be before there's a serious risk of hypothermia.
While lab testing simulates how a sleeping bag should be used, it can't account for all the variables that a lab can't simulate. For example, differences in people's clothing, gear, body types, metabolism, age, food eaten, weather conditions, and more. So, when you use your sleeping bag in the outdoors, its comfort level will probably differ from its tested temperature rating.
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Physiological differences between genders
Sleeping bag temperature ratings are based on standardised tests, which provide three temperature thresholds: a comfort rating, a limit rating, and an extreme rating. The comfort rating is based on the air temperature at which the "average female" can sleep comfortably through the night, while the limit rating is based on the temperature at which the "average man" can maintain his thermal equilibrium in a curled-up position. The extreme rating indicates how cold the air could be before there is a serious risk of hypothermia or death.
Women's sleeping bags typically have more insulation than men's bags, making them roughly 10–15 degrees Fahrenheit warmer than similarly rated men's bags. This is because the average woman sleeps colder than the average man due to physiological differences such as lower metabolic rates and muscle mass. Women's sleeping bags are also usually narrower in the shoulders and wider in the hips than men's or unisex bags.
However, it's important to remember that individual preference, metabolism, age, clothing, gear, weather conditions, and other factors can also affect how warm or cold we sleep. Therefore, the temperature ratings on sleeping bags are estimates and may not match the real-world comfort levels experienced by all users.
To find the old sleeping bag cold ratings, you can look for the EN (European Norm) or ISO (International Standards Organization) ratings, which indicate lab-tested temperature ratings. These ratings are useful for comparing sleeping bags from different brands. However, keep in mind that real-world comfort may differ due to various variables that a lab cannot simulate. Additionally, older sleeping bags may not have been tested using standardised methods, as brands previously tested their bags in their own labs using different methods.
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Individual factors that affect warmth
Sleeping bag temperature ratings are based on standardised tests, such as the ISO test, which provides three temperature thresholds: comfort, limit, and extreme. However, these ratings are only estimates, and individual factors can affect how warm or cold you feel when using a sleeping bag.
One of the most important individual factors is your body's metabolism, which is influenced by physiological differences. For example, women generally sleep colder than men due to their lower metabolic rate and muscle mass. As a result, women's sleeping bags typically have a comfort rating, indicating the temperature at which a cold sleeper might feel comfortable. In contrast, men's sleeping bags usually have a lower limit rating, which is the temperature at which a warm sleeper can still be comfortable.
Your individual preference, age, and body type can also affect your warmth levels when using a sleeping bag. Some people tend to feel colder or warmer than others, regardless of the external temperature. Additionally, the size of the sleeping bag can make a difference. A wider bag means more air space that your body must heat, while a bag that is too small can feel constricting and lead to compression, reducing warmth.
Other factors that can influence your warmth include what you eat and drink, your clothing and gear, and the environmental conditions. For instance, the temperature and humidity of the external environment can impact the thermal properties of the sleeping bag. Furthermore, the material and manufacturing technique of the sleeping bag can also affect its insulating properties.
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Season and temperature ratings
Sleeping bag temperature ratings are a complicated subject. They are based on standardised tests that provide three temperature thresholds: a comfort rating, a limit rating, and an extreme rating. However, these ratings are estimates and are based on ''average' users, so they should be used as a guide.
The comfort rating is the temperature at which a cold sleeper might feel comfortable. This is the temperature rating used for women's bags, as data shows that the "average woman" will feel colder in the same bag as the "average man". The limit rating is the temperature at which a warm sleeper might still feel comfortable. This is the temperature rating used for men's bags. The extreme rating gives an idea of how cold the air could be before there is a serious risk of death from hypothermia.
In addition to these temperature ratings, sleeping bags are also rated by the number of seasons they are suitable for. One-season sleeping bags are designed for summer camping and backpacking, with temperatures above 5° Celsius/Centigrade or 40° Fahrenheit. 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 temperatures might dip just below freezing (down to -5°C or approximately 20°F). Four-season sleeping bags are designed for winter use when there is frost or snow on the ground and night-time temperatures drop to around 10°C or 15°F. The term ''five-season' is sometimes used to indicate a sleeping bag designed for expedition or high-altitude use in extremely cold temperatures ranging from -10°C to -40°C.
When choosing a sleeping bag, it is important to consider not only the temperature rating but also the R-value of the sleeping pad. The sleeping pad insulates the sleeper from the ground, which can be cold or freezing. A higher R-value indicates more insulation. For example, a summer pad might have an R-value of less than 1, while a winter pad might have an R-value of 8 or higher. Most 3-season backpacking pads have R-values between 2 and 4.
It is also worth noting that real-world comfort will probably differ from a sleeping bag's tested temperature rating. Lab testing cannot account for all the variables that affect how warm or cold a person sleeps, such as differences in clothing, gear, body type, metabolism, age, and food intake. Therefore, it is always good to prepare properly before spending a night sleeping outside. Check the weather and leave a safe margin between expected nighttime lows and your bag's rating.
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Frequently asked questions
The temperature rating of your sleeping bag should be printed on the bag itself or on a tag attached to it. The rating systems in use include EN and ISO.
The EN and ISO ratings are the results of standardised tests that determine the thermal resistance of a sleeping bag. The ISO test involves placing a manikin, wearing standard pyjamas and a cold-weather mask, inside the sleeping bag, which is then placed inside a climate-controlled room. The manikin measures the power needed to maintain warmth in the cold room.
The temperature rating of your sleeping bag should give you an indication of the temperature range for which it is suitable. For example, a two-season sleeping bag is designed for slightly cooler nights in spring and summer, with a temperature range of 0 to +5°C. A three-season bag is designed for colder nights throughout spring, summer and autumn, when temperatures might dip just below freezing. A four-season bag is designed for winter use when there is frost or snow on the ground and temperatures will drop to around +15°F (-10°C).
The temperature rating of your sleeping bag is a good guide, but it's important to remember that other factors can affect how warm you sleep. These include what you eat and when you eat it, how much you've drunk, what you're wearing, and how accustomed you are to sleeping outdoors. The shape, features and age of your sleeping bag will also play a part in how closely it lives up to expectations.
If your sleeping bag is damaged, or no longer provides the warmth you need, it may be time to replace it.
