Herbie Murray
Sleeping bags are rated according to their warmth and suitability for different conditions. The key factor when choosing a sleeping bag is its temperature rating, which indicates the lowest temperature at which the bag will keep a person warm. This is determined through standardized testing, such as the ISO Test, which 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 female can sleep comfortably, while the limit rating is based on the temperature at which the average male can maintain thermal equilibrium. In addition to temperature ratings, sleeping bags also have season ratings, which indicate the time of year for which the bag is most suitable. For example, a three-season bag can be used throughout spring, summer, and autumn. Understanding these ratings is essential for choosing the right sleeping bag for your needs.
| Characteristics | Values |
|---|---|
| Key factor | Temperature rating |
| Temperature ratings | Estimates, not exact |
| Lab testing | Standardized, but doesn't account for all real-world variables |
| Numbers on bag names | Don't match exact temperature ratings |
| Women's sleeping bags | Use the comfort rating as women tend to feel colder |
| Season rating | Indicates the time of year for which a sleeping bag is most suitable |
| Three-season sleeping bags | Designed for colder nights throughout spring, summer, and autumn |
| Four-season sleeping bags | Designed for winter use |
| Standardized testing | Provides comfort, limit, and extreme ratings |
| Comfort rating | Based on the air temperature at which the "average female" can sleep comfortably |
| Limit rating | Based on the temperature at which the "average man" can maintain thermal equilibrium in a curled-up position |
| Type of insulation | Down vs. synthetic |
| Weight | Quality of insulation and the cut of the bag |
| R-value of the sleeping pad | Appropriate for expected ground temperatures |
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What You'll Learn
Sleeping bag temperature ratings are estimates
Sleeping bag temperature ratings are only estimates of how warm the sleeper will be in a given bag. The ratings are determined by standardised tests, such as the ISO test, which involve placing a heavily instrumented electronic mannequin, dressed in long underwear, inside the sleeping bag, and measuring the amount of electrical energy needed to maintain the mannequin's initial temperature as the air temperature drops.
However, there are several limitations to these tests. Firstly, they assume that all sleepers are average sleepers, either male or female, and do not account for individual variations in body type, clothing, gear, and sleeping habits. For example, the comfort rating, which is typically assigned to women's bags, assumes that the average woman will feel colder than the average man and requires more insulation to stay warm. However, not all women will fit this average, and some may find that a bag with a lower temperature rating is more comfortable for them.
Additionally, the tests do not account for changing weather conditions, differences in food intake, or other external factors that can affect a person's comfort level when using a sleeping bag in the real world. The temperature ratings are also rounded to the nearest 0 or 5, which can be misleading as the actual temperature rating may be slightly higher or lower than the advertised rating.
Therefore, it is important to understand that the temperature ratings on sleeping bags are only estimates and may not perfectly match an individual's comfort level in all situations. When choosing a sleeping bag, it is recommended to select one with a temperature rating slightly lower than the typical low temperatures you anticipate encountering, as you can always open up the bag to cool down if needed. Additionally, consider other factors such as the R-value of your sleeping pad and the type of insulation in the bag to ensure a comfortable sleeping experience.
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Lab testing simulates how a sleeping bag is used
When it comes to choosing a sleeping bag, temperature ratings are a key factor. Sleeping bags are assigned temperature ratings through standardised testing, which provides consumers with a useful guide. However, it's important to remember that these ratings are estimates and not exact guarantees of warmth. Lab testing simulates how a sleeping bag should be used, but there are limitations to the process.
The ISO Test is the standardised test used to rate sleeping bags. This test involves placing an electronic mannequin, dressed in long underwear and socks, inside the sleeping bag, which is placed on a foam sleeping pad. The air temperature is then lowered, and the amount of electrical energy required to maintain the mannequin's initial temperature is measured. The more energy needed to keep the mannequin warm, the less effective the sleeping bag is considered to be.
The ISO 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 female" 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 thermal equilibrium in a curled-up position. This means that the average man will not be in danger of hypothermia, but may not be completely comfortable.
While the ISO Test provides a standardised method for rating sleeping bags, it's important to remember that individual factors can affect the warmth and comfort of a sleeping bag in real-world use. These factors include differences in body types, metabolism, clothing, sleeping pads, weather conditions, and more. Therefore, the temperature rating of a sleeping bag should be considered a guide, and consumers should choose a bag that is suitable for the expected weather conditions and their personal preferences.
In addition to the temperature rating, other factors to consider when choosing a sleeping bag include the type of insulation (down vs synthetic), the weight of the bag, and the seasonality or intended use of the bag. For backpacking, a lightweight and efficient bag that provides warmth without adding too much bulk is ideal. On the other hand, a camping bag can be larger and heavier, as it doesn't need to be carried in a pack.
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Women's sleeping bags use the comfort rating
The key factor when choosing a sleeping bag is its temperature rating. Sleeping bags are assigned temperature ratings based on standardised testing, which provides three temperature thresholds: a comfort rating, a limit rating, and an extreme rating. The comfort rating is the temperature at which the "average female" can sleep comfortably through the night without having to curl up in a ball for warmth. It is designed for colder sleepers and is, therefore, the specification target for women's bags.
The comfort rating is also known as the temperature rating a female sleeper should orient themselves with. It is the lowest temperature at which a sleeping bag is likely to provide a cosy night's sleep. The limit rating, on the other hand, is the temperature at which the "average man" can maintain his thermal equilibrium in a curled-up position. This means that the "average man" won't necessarily be comfortable at this temperature, but he can sleep without shivering and is not in danger of hypothermia.
Lab-tested temperature ratings (indicated by "EN" or "ISO" ratings) are useful for comparing sleeping bags from different brands. However, real-world comfort may differ from lab-tested temperature ratings due to various factors, including differences in people's clothing, gear, body types, weather conditions, and food intake. Therefore, it is important to understand how the ratings work and consider your individual needs when choosing a sleeping bag.
In addition to the comfort and limit ratings, sleeping bags may also have a season rating, which indicates the time of year for which the bag is most suitable. For example, a one-season bag is designed for summer use, while a three-season bag can be used throughout spring, summer, and autumn. It is important to consider both the temperature and season ratings when selecting a sleeping bag to ensure it is suitable for your needs.
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Season ratings indicate the time of year a bag is suitable for
Season ratings indicate the time of year a sleeping bag is suitable for. They correspond to the four seasons: spring, summer, autumn, and winter, or a combination of these. Sleeping bag ratings are designed to make it easier to choose the right bag for your needs.
A one-season bag is designed for summer use, with temperatures staying above 5° Celsius/Centigrade (C) or approximately 40° Fahrenheit (F). They are also suitable for bunkhouses, huts, hostels, and camper vans. Two-season sleeping bags are designed for slightly cooler nights in spring and summer, with a temperature range of 0 to 5°C (30 to 40°F). They are also suitable for milder autumn nights or 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 20°F). They offer a good balance between warmth, weight, and bulk, making them versatile for a range of camping and backpacking trips. Four-season sleeping bags are designed for winter use, with temperatures dropping to around -10°C or 15°F. They are optimised for cold conditions and may be too warm for milder seasons.
It's important to note that temperature ratings are estimates, and real-world comfort may differ from lab-tested ratings due to variations in clothing, gear, body types, weather conditions, and other factors. Additionally, women's sleeping bags typically have more insulation and are rated differently than men's bags due to physiological differences in temperature regulation.
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The ISO test provides three temperature thresholds
The COMFORT rating is based on the air temperature at which the "average female" can sleep comfortably through the night without having to curl up in a ball for warmth. If you tend to sleep cold, you should pay close attention to a bag’s COMFORT rating. This is the lowest temperature at which your bag is likely to provide a cosy night’s sleep.
The LIMIT rating is based on the temperature at which the "average man" can maintain his thermal equilibrium in a curled-up position. This means that the "average man" won't necessarily be comfortable at this temperature, but he can sleep without expending energy shivering and is not in danger of hypothermia. A more general way of interpreting this data is to apply it to warm sleepers.
The LIMIT rating is generally the temperature assigned to men's or unisex bags, while the COMFORT rating is usually assigned to women's bags. This is because data on physiological differences between traditional genders has shown that the "average woman" will feel colder in the same bag than the "average man". Women's bags therefore tend to have more insulation, making them roughly 10–15 degrees Fahrenheit warmer than similarly rated men’s bags.
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Frequently asked questions
The temperature rating. This indicates the warmth of the bag and its suitability for different conditions.
There are three types of temperature ratings: comfort, limit, and extreme. The comfort rating is the lowest temperature at which the bag will keep a "cold sleeper" comfortable and is generally used for women's bags. The limit rating is the lowest temperature at which the bag will keep a "warm sleeper" comfortable and is generally used for men's or unisex bags. The extreme rating is the lowest temperature at which the bag will keep a person alive without causing hypothermia.
Consider the season you will be using the sleeping bag in. A one-season bag is designed for summer use, a two-season bag is designed for spring and summer, a three-season bag is designed for spring, summer, and autumn, and a four-season bag is designed for winter. Additionally, pay attention to the comfort and limit ratings to ensure the bag is suitable for your sleeping habits and body type.
