Gina Johnson
Sleeping bag temperature ratings are a complicated topic, with many factors influencing the warmth of a sleeping bag. The key factor when choosing a sleeping bag is its temperature rating, which is determined by standardised testing, such as the ISO test. The ISO test uses a heated mannequin with temperature sensors in a climate-controlled room to determine the sleeping bag's thermal resistance. The test provides three temperature thresholds: comfort rating, limit rating, and extreme rating. However, it's important to note that these ratings are based on 'average' users and may not apply to everyone due to individual differences in metabolism, age, and other factors. Additionally, the fit of the sleeping bag, the user's clothing, and other variables can also impact the actual temperature experienced when using the bag.
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What You'll Learn
Sleeping bag temperature ratings are estimates
The ISO test provides three temperature thresholds: a comfort rating, a limit rating, and an extreme rating. The comfort rating is the temperature at which the "average" woman can sleep comfortably without curling up for warmth. The limit rating is the temperature at which the "average" man can maintain thermal equilibrium in a curled-up position without shivering. The extreme rating indicates the temperature at which there is a serious risk of hypothermia for a "standard" woman.
It's important to note that these ratings are based on "average" users and should be used as a guide. Individual factors such as metabolism, age, body shape, clothing, and sleeping environment can significantly impact how warm a person sleeps. Additionally, the fit of the sleeping bag and the quality of the sleeping mat can also affect its warmth.
When choosing a sleeping bag, it's essential to consider not only the temperature ratings but also other factors such as cost, pack size, and fill material. Season ratings are also used to indicate the time of year for which a sleeping bag is most suitable, such as three-season bags for spring, summer, and autumn, or four-season bags for winter use.
While temperature ratings provide a baseline for comparison, they are estimates and may not accurately predict how warm a sleeping bag will be for a specific individual. It's always a good idea to be prepared with extra layers, a fire source, or other means of staying warm in case the sleeping bag is not sufficient.
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ISO 23537 standards and comfort ratings
The ISO 23537 standard (also known as EN 13537) is a widely used international standard for measuring sleeping bag temperature ratings. It was established by the International Standards Organization in 2016 to replace the previous European Norm (EN) standard and make it more consistent.
The ISO 23537 standard includes three temperature thresholds to help guide consumers in choosing the right sleeping bag: a Comfort rating, a Limit rating, and an Extreme rating. The Comfort rating is based on the temperature at which the "average woman" can sleep comfortably through the night without curling up for warmth. The Limit rating is based on the temperature at which the "average man" can maintain his thermal equilibrium in a curled-up position without shivering. The Extreme rating indicates the temperature at which there is a serious risk of death from hypothermia within a matter of hours.
It's important to note that the ISO 23537 standard is based on lab testing, which may not account for all real-world variables. For example, it doesn't consider factors such as differences in people's clothing, gear, body types, weather conditions, and metabolism, all of which can affect the comfort level of a sleeping bag in outdoor conditions. Therefore, the actual comfort level of a sleeping bag may differ from its lab-tested temperature rating.
Additionally, the ISO 23537 test does not cover all the features that can affect warmth retention. For example, it doesn't fully test draft-prevention features such as hoods, neck collars, and zipper draft tubes, which can impact the overall warmth of the sleeping bag. Other design issues, such as insulation movement, overstuffing, and balancing between comfort and heating, can also affect the warmth retention of the sleeping bag.
Despite these limitations, the ISO 23537 standard provides a useful framework for comparing different sleeping bags and ensuring a certain level of performance in terms of protection against the cold. It is based on extensive human research and helps curb unrealistic marketing claims, providing consumers with more accurate information about the product's capabilities.
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Lab-tested temperature ratings
Sleeping bag temperature ratings are a complicated subject, and it's important to understand how bags are tested for warmth in a lab to make sense of the numbers you see on sleeping bags. Lab-tested temperature ratings, indicated by "EN" or "ISO" ratings, are useful for making direct comparisons between sleeping bags from different brands.
The EN and ISO tests use a heated mannequin dressed in a base layer, tights, long socks, and a hat, placed inside the sleeping bag, which is then placed on an insulated sleeping pad in a cold chamber. Measurements are taken at multiple points on the surface of the mannequin to see how much energy per given area is necessary to maintain standard skin temperature. The results are used to calculate the EN or ISO temperature ranges and limits.
The EN 13537 standard, updated in 2017 to ISO 23537, offers four different temperature ratings: Upper Comfort, Comfort, Limit, and Extreme. The Comfort rating is based on the temperature at which the "average woman" can sleep comfortably for eight hours without curling up for warmth. The Limit rating is based on the temperature at which the "average man" can maintain thermal equilibrium in a curled-up position without shivering. The Extreme rating indicates a survival rating that does not rule out frostbite.
It's important to note that these ratings are based on 'average' users and should be used as a guide. Real-world comfort may differ from lab-tested temperature ratings due to various factors, such as differences in clothing, gear, body types, and weather conditions, and individual preferences.
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How to interpret the data
Sleeping bag temperature ratings are based on standardised tests, such as the ISO 23537 test, which replaced the EN 13537 test. The ISO test uses a heated mannequin with multiple temperature sensors inside a climate-controlled room on a standardised mat. The mannequin, wearing standard pyjamas and a cold-weather mask, measures the power needed to maintain warmth in a cold room, determining the sleeping bag's thermal resistance.
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 woman" can sleep comfortably through the night without curling up in a ball for warmth. The limit rating is based on the temperature at which the "average man" can maintain his thermal equilibrium in a curled-up position. The limit temperature is the number most retailers and brands refer to. The extreme rating gives an idea of the temperature at which there is a serious risk of death from hypothermia within a few hours.
It's important to note that these ratings are based on "average" users and should be used as a guide, as individual factors such as metabolism, age, and personal preference can affect how warm or cold someone sleeps. Additionally, the fit of the sleeping bag, the type of sleeping mat, and the user's clothing can also impact the warmth of the sleeping bag. Therefore, it is recommended to consider the actual test rating on the bag rather than merely the number in its name.
When interpreting the data, it's also worth considering the seasonality of the sleeping bag. Three-season sleeping bags are designed for spring, summer, and autumn, while four-season bags are for winter use. Additionally, the term "five-season" is used for bags designed for expedition or high-altitude use in extremely cold temperatures.
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Season ratings and temperature ranges
Sleeping bag temperature ratings can be confusing and are influenced by several factors. The numbers on sleeping bags are marketing choices and are not exact temperature ratings. The ISO test is recognised globally and uses a heated mannequin with multiple temperature sensors in a climate-controlled room to determine the bag's thermal resistance. The test provides three temperature thresholds: a comfort rating, a limit rating, and an extreme rating. The comfort rating is based on the temperature at which the "average woman" can sleep comfortably without curling up for warmth. The limit rating is based on the temperature at which the "average man" can maintain thermal equilibrium in a curled-up position without shivering. The extreme rating indicates the temperature at which there is a serious risk of hypothermia.
In addition to temperature ratings, sleeping bags also have season ratings. A three-season sleeping bag is designed for spring, summer, and autumn, when temperatures may dip just below freezing. Four-season sleeping bags are designed for winter use, with temperatures dropping to around -10°C or 15°F. Five-season sleeping bags are for expeditionary use and can handle extremely cold temperatures, ranging from -10°C to -40°C.
It's important to remember that temperature and season ratings are based on "average" users and should be used as a guide. Individual factors such as metabolism, age, and sleep patterns can affect how warm or cold someone sleeps. Other considerations when choosing a sleeping bag include cost, pack size, and fill material.
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Frequently asked questions
The numbers on sleeping bags refer to their temperature ratings, which indicate the range of temperatures that a sleeping bag is suitable for.
Sleeping bags are assigned temperature ratings through standardised testing, such as the ISO 23537 test. This test uses a heated mannequin with temperature sensors inside a climate-controlled room to determine the sleeping bag's thermal resistance.
There are three main types of temperature ratings: Comfort, Limit, and Extreme. The Comfort rating is based on the temperature at which the "average woman" can sleep comfortably. The Limit rating is based on the temperature at which the "average man" can maintain thermal equilibrium in a curled-up position. The Extreme rating indicates the temperature at which there is a serious risk of hypothermia.
When choosing a sleeping bag, consider the expected temperatures and whether you tend to sleep hot or cold. Select a bag with a rating that is lower than the lowest temperature you expect. Additionally, pay attention to the type of rating that best suits your needs, such as the Comfort rating if you tend to sleep cold or the Limit rating if you sleep warm.
