Gina Johnson
Sleeping bag temperature ratings are a complicated topic. While they provide a useful guide for consumers, they are not always accurate in real-world conditions. The ISO Test, which is recognised globally, provides three temperature thresholds: comfort, limit, and extreme. The comfort rating is based on the temperature at which the average female can sleep comfortably, while the limit rating is based on the temperature at which the average man can maintain thermal equilibrium without excessive perspiration. However, these ratings don't account for individual variations, such as body type, clothing, and external factors like weather conditions. Additionally, the numbers on bag names might not always match the actual temperature ratings, and it's important to consider other factors like the R-value of the sleeping pad. Some companies also offer their own ratings, which may be more or less trustworthy. Ultimately, while temperature ratings provide a starting point, other factors should also be considered when choosing a sleeping bag.
| Characteristics | Values |
|---|---|
| Key factor when choosing a sleeping bag | Temperature rating |
| --- | --- |
| Protocols | ISO 23537 test |
| ISO test procedure | A thermal mannequin is placed inside the sleeping bag, which is placed on a standard foam roll mat. The temperature of the air is then lowered, and the amount of electrical energy needed to maintain the mannequin's initial temperature is measured. |
| ISO test results | Three temperature thresholds: comfort, limit, and extreme ratings |
| Limitations of the ISO test | Does not account for variations in clothing, gear, body types, weather conditions, etc. |
| Limitations of temperature ratings | Numbers on bag names do not always match exact temperature ratings. |
| Recommendations | Choose a bag with a comfort rating that is lower than the lowest expected temperature. |
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What You'll Learn
Limitations of lab testing
While lab testing has standardised the process of determining temperature ratings for sleeping bags, there are still some limitations to this method. Firstly, lab-tested temperature ratings may not accurately reflect real-world comfort due to the numerous variables that a lab cannot simulate. These variables include differences in people's clothing and gear, body types, metabolic rates, and food intake, as well as changing weather conditions. For example, the ISO 23537 test simulates a 1 kmph airflow, which may not accurately represent real-world conditions and can negatively affect the results for very air-permeable fabrics.
Additionally, the temperature ratings on sleeping bags are estimates and should be used as a guide. The comfort and lower-limit ratings are based on average female and male sleepers, respectively, but individual preferences and experiences may vary. For instance, some people may sleep hot or cold, or have different comfort levels in different sleeping positions. The ratings also assume the use of a sleeping pad, which can affect the overall comfort and warmth experienced by the sleeper.
Furthermore, the naming of sleeping bags may not always match their exact temperature ratings. Manufacturers may round up or down to a number that ends in 0 or 5 for simplicity, so it is important to look at the actual test rating on the bag. Lastly, it is worth noting that temperature ratings do not account for extreme climate conditions, and their accuracy diminishes below certain temperatures, such as -15°C for the ISO 23537 test.
To overcome these limitations, it is recommended to consider individual factors such as one's metabolism, clothing, gear, and sleeping pad when choosing a sleeping bag. Additionally, seeking recommendations from experienced friends, shop staff, or trusted brands can provide valuable insights beyond temperature ratings.
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Differences in individual preferences and physiology
Sleeping bag temperature ratings are based on standardised laboratory tests that produce a rating range for each sleeping bag. However, these ratings are only estimates, and there are several factors that can affect an individual's comfort when using a sleeping bag.
One important factor is an individual's preference and physiology. People have different preferences for sleeping temperatures, and some people may prefer a warmer or cooler sleeping environment. Additionally, physiological differences between individuals can also affect their comfort. For example, women tend to sleep colder than men, and therefore, women's sleeping bags typically have more insulation and are rated for lower temperatures than men's bags.
Another factor that can affect comfort is an individual's body type and sleeping habits. People who sleep hot or cold will have different comfort levels, and the bag's fit can also impact how well it retains heat. A person's body shape and size can affect how much air circulates inside the bag and how well the bag can trap body heat.
It's worth noting that the temperature ratings on sleeping bags are based on the assumption that the user is dressed in appropriate clothing and using a suitable sleeping pad. The type and amount of clothing worn, as well as the insulating properties of the sleeping pad, can significantly impact the overall comfort of the sleeper. Therefore, it's important to consider these additional factors when choosing a sleeping bag and preparing for a night of sleeping outdoors.
Lastly, individual differences in metabolism and circulation can also play a role in how well a person retains body heat. People with higher metabolisms or better circulation may feel warmer in a sleeping bag than those with slower metabolisms or poorer circulation. Additionally, factors such as diet and physical activity levels can also influence an individual's comfort when sleeping in a bag rated for a specific temperature range.
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The three rating categories
Sleeping bag temperature ratings are a complicated subject. While they provide a useful guide for consumers, they are not entirely accurate. This is due to the many variables that a lab cannot simulate.
- International standards from EN or ISO: These are standardised laboratory tests that produce a rating range for each sleeping bag, with two temperature ratings within that range: a comfort rating and a lower-limit rating. The comfort rating indicates the temperature at which a cold sleeper might feel comfortable, and the lower-limit rating is always lower than the comfort rating and indicates the temperature at which a warm sleeper might still be comfortable. The ISO test involves placing a thermal mannequin, dressed in long underwear, inside the sleeping bag, which is then placed on a sleeping pad. The temperature of the air is then lowered, and the amount of electrical energy needed to maintain the mannequin's initial temperature is measured. This test has been correlated with real-world outcomes and can help predict the level of comfort a person can expect from the bag. However, it does not account for all variables, such as differences in body types, clothing, and weather conditions.
- Trustworthy homebrew ratings (usually from cottage companies): Some smaller companies may develop their own rating systems or use variations of the EN or ISO tests. These ratings may still be accurate but may not be directly comparable to the standardised tests.
- Untrustworthy companies who cheat the system: Unfortunately, some companies may mislead consumers by providing inaccurate temperature ratings. It is essential to research and trust reputable manufacturers when purchasing a sleeping bag.
It is worth noting that sleeping bag temperature ratings are just estimates, and real-world comfort may differ from the tested temperature rating. When choosing a sleeping bag, it is recommended to consider your personal preferences, whether you tend to sleep warm or cold, and the expected weather conditions. Additionally, other factors such as the fit of the bag, the quality of the sleeping pad, and the insulation of the bag can also impact your comfort.
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How to prepare for a night's sleep outdoors
Sleeping outdoors? Here's how to prepare for a good night's sleep.
First, you'll need to choose a sleeping bag. Temperature ratings are a key factor when making your selection. Sleeping bags are typically given a standardised temperature rating through laboratory testing, which involves placing a thermal mannequin inside the bag to measure how insulating it is at various temperatures. However, it's important to remember that these ratings are only estimates, and the comfort level you experience outdoors may differ from the tested rating due to various variables that a lab can't simulate. For example, the rating doesn't account for differences in body types, clothing, gear, and weather conditions.
When choosing a sleeping bag, look for one with a temperature rating that is lower than the expected nighttime lows. For example, if you're expecting temperatures of 20°F, get a bag with a comfort rating of 15°F or 20°F. Additionally, consider your own preferences and tendencies—if you're a cold sleeper or tend to feel chilly, add 10 degrees to the expected temperature when selecting a bag.
It's also important to pay attention to the type of sleeping bag you choose. Women's sleeping bags typically have more insulation and are rated for temperatures that are 10-15 degrees Fahrenheit warmer than similarly-rated men's bags, as they are designed for women, who tend to sleep colder than men on average. However, this is just a general guideline, and you should choose a bag that suits your individual needs and preferences.
Aside from a sleeping bag, you'll also need a proper sleeping pad. A good sleeping pad will provide insulation and ensure that your sleeping bag keeps you warm enough. Look for a pad with an R-value that is appropriate for the expected ground temperatures.
Lastly, always check the weather forecast before heading out, and be prepared for changing weather conditions. By following these tips, you can maximise your chances of a comfortable night's sleep outdoors.
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The accuracy of ISO 23537 testing in extreme climates
The ISO 23537 standard has brought consistency to the way sleeping bags are tested and labelled, which has helped consumers make more accurate comparisons between products. However, the accuracy of the ISO 23537 test in extreme climates is questionable due to the limitations of standardised laboratory testing.
The ISO 23537 test involves placing a heated or electronic mannequin, dressed in long underwear, inside a sleeping bag on top of a foam pad. The mannequin is extensively calibrated with mathematical models, but it does not account for all human variations. For instance, the mannequin does not factor in differences in body types, clothing and gear, and food intake, which can affect a person's comfort level.
The test also does not apply to sleeping bags designed for specific purposes, such as military use and extreme climate zone expeditions. The limit temperature for extreme climate conditions is set at −20 °C, but there is no prediction model for determining the limiting temperatures for children's and babies' sleeping bags due to ethical reasons.
While the ISO 23537 test provides a standardised method for assessing sleeping bags, real-world comfort may differ from the tested temperature ratings. Consumers should consider the ISO test as a guide and use their judgement when choosing a sleeping bag suitable for their needs. For instance, women and cold sleepers may need to add 10 degrees to the comfort rating to ensure a cosy night's sleep.
In conclusion, while the ISO 23537 test provides a more consistent and trustworthy means of comparing sleeping bags, its accuracy in extreme climates is limited due to the inherent simplifications of laboratory testing. Consumers should consider various factors beyond the ISO ratings to ensure they purchase a sleeping bag that meets their specific needs and comfort levels.
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Frequently asked questions
Sleeping bag temperature ratings are a standardised way of indicating how warm a sleeping bag will keep you.
Sleeping bags are tested in a laboratory using a thermal mannequin dressed in long underwear and placed on a foam sleeping pad. The temperature of the air is then lowered, and the amount of electrical energy needed to maintain the mannequin’s initial temperature is measured.
There are three main types of temperature ratings: comfort, limit, and extreme. The comfort rating indicates the temperature at which a cold sleeper might feel comfortable, the limit rating indicates the temperature at which a warm sleeper might still be comfortable, and the extreme rating indicates the lowest temperature at which the bag will protect you from hypothermia.
While sleeping bag temperature ratings provide a useful guide, they may not always be accurate in real-world situations. This is because there are many variables that affect how warm a person will feel in a sleeping bag, such as body type, clothing, and weather conditions.
When choosing a sleeping bag, it is important to consider your own personal preferences and whether you tend to sleep hot or cold. It is generally recommended to choose a bag with a comfort rating that is slightly lower than the lowest temperature you expect to encounter.
