Ashwin Lewis
A good sleeping bag can make all the difference when camping. The key factor when choosing a sleeping bag is its temperature rating. Sleeping bags are now rated according to the International Organization for Standardization standard, using ISO 23537 (the ISO Test). The ISO test involves placing a heavily instrumented electronic mannequin, dressed in long underwear, inside the sleeping bag in question, and positioning both on top of 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. However, it's important to remember that temperature ratings are estimates, and real-world comfort may differ due to various factors such as clothing, gear, body type, weather conditions, and food intake. To determine the right sleeping bag for you, consider factors such as insulation type, fill power, and gender-specific ratings, as women's sleeping bags typically have more insulation than men's bags.
| Characteristics | Values |
|---|---|
| Key factor | Temperature rating |
| Temperature ratings | Estimates, not exact |
| Lab testing | Simulates how a sleeping bag is used |
| Lab-tested temperature ratings | Useful for making comparisons between sleeping bags from different brands |
| Real-world comfort | May differ from lab-tested temperature ratings |
| Numbers on bag names | Don't match exact temperature ratings |
| Women's sleeping bags | Use the comfort rating |
| ISO Test | Provides three temperature thresholds: comfort, limit, and extreme |
| 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 |
| Unisex sleeping bag | Will have a lower limit and a comfort limit |
| Sleeping bag warmth | Affected by a variety of factors, including insulation and sleeping pads |
| Insulation types | Down and synthetic |
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What You'll Learn
Sleeping bag temperature ratings are estimates, not exact
Sleeping bag temperature ratings are based on estimates and are not an exact science. The ISO (International Standards Organization) test is the standard method used to determine the temperature ratings of sleeping bags. This test involves placing a heavily instrumented electronic mannequin, dressed in long underwear, inside the sleeping bag, which is then 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.
While this standardized test provides a general guideline for consumers, it is important to remember that it has limitations and may not perfectly predict an individual's comfort level. Several factors can affect one's comfort when using a sleeping bag, including clothing and gear, body type, weather conditions, and food intake. Additionally, the numbers on bag names may not always match the exact temperature ratings, as brands may round up or down for simplicity.
The ISO Test provides three temperature thresholds: the COMFORT rating, the LIMIT rating, and the EXTREME rating. The COMFORT rating is based on the temperature at which the "average female" can sleep comfortably without curling up for warmth. If you tend to sleep cold, this rating is essential to consider. The LIMIT rating, on the other hand, is the temperature at which the ""average man" can maintain thermal equilibrium in a curled-up position. This rating is relevant if you are a warm sleeper. The EXTREME rating indicates the risk of hypothermia and is not recommended for sole reliance in survival situations.
It is worth noting that sleeping bag temperature ratings are designed to provide a baseline for comparison. While they offer valuable guidance, they may not guarantee that a specific bag will keep you warm at a particular temperature. Therefore, it is always advisable to prepare properly for outdoor sleeping, including checking the weather and choosing a bag with an appropriate temperature rating for the expected conditions.
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Lab testing conditions may not match real-world usage
Lab testing protocols typically involve placing a test dummy or an electronic mannequin dressed in base layers into the sleeping bag, which may not account for variations in people's clothing, gear, body types, and sleeping habits (warm or cold sleepers). Additionally, factors such as changing weather conditions and individual metabolic rates can also impact your comfort level.
The temperature ratings on sleeping bags are estimates, and the numbers on the bag names may not always match the exact temperature ratings. For example, a bag named "Snugglebuggle 15 Bag" might have an ISO lower-limit rating of 18 degrees Fahrenheit. Brands often round up or down to a number ending in 0 or 5 for simplicity.
Physiological differences between traditional genders also play a role in temperature ratings. Women's sleeping bags typically use the comfort rating, as the "average woman" tends to feel colder than the "average man" in the same bag. Women's bags usually have more insulation, making them warmer than similarly-rated men's bags. However, these are generalizations, and individual preferences and metabolic rates can vary significantly.
It's important to remember that temperature ratings are just guidelines, and your real-world experience may differ. To ensure a comfortable night's sleep, consider factors such as your sleeping habits, the outdoor temperature, the use of additional insulation or sleeping liners, and your individual preferences. Testing out your sleeping bag in a controlled environment, like your backyard, can also help you determine its effectiveness before venturing into the wilderness.
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Women's sleeping bags use the comfort rating
When it comes to choosing a sleeping bag, the key factor is its temperature rating. Sleeping bags are designed and rated based on standardised testing, such as the ISO (International Standards Organisation) Test, which involves placing a heavily instrumented electronic mannequin, dressed in long underwear, inside the sleeping bag, and measuring the amount of electrical energy needed to maintain its initial temperature as the air temperature is lowered. This 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 without curling up for warmth. This rating is used for women's sleeping bags because data has shown that the "average woman" will feel colder in the same bag as the "average man". Women's sleeping bags typically have more insulation, making them roughly 10–15 degrees Fahrenheit warmer than similarly-rated men's bags.
The limit rating, on the other hand, is based on the temperature at which the "average man" can maintain his thermal equilibrium in a curled-up position. This means that he won't be comfortable, but he won't be shivering and won't be in danger of hypothermia. This rating is used for men's sleeping bags, which generally weigh less than women's bags at the same temperature due to the use of the comfort rating for women's bags.
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, not all sleeping bags have an ISO or EN rating, and brands might not choose to get ISO testing for bags intended for mild conditions or casual use. Therefore, it's essential to consider your personal preferences, sleeping habits, and the expected weather conditions when choosing a sleeping bag.
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The ISO test provides three temperature thresholds
Sleeping bags are assigned temperature ratings based on the ISO test, which provides three temperature thresholds: a comfort rating, a limit rating, and an extreme rating. These ratings are based on the understanding that sleep comfort is a personal preference and that people sleep differently at night. The ISO test helps guide users by providing a range of temperature ratings to choose from.
The comfort rating is based on the air temperature at which the "average female" can sleep comfortably through the night without curling up in a ball for warmth. This rating is targeted at colder sleepers, typically women, as data shows that the "average woman" will feel colder in the same bag as the "average man." Sleeping bags for women tend to have more insulation, making them 10-15 degrees Fahrenheit warmer than similarly-rated men's bags.
The limit rating is the temperature at which the "average man" can maintain his thermal equilibrium in a curled-up position. At this temperature, the average man will not be comfortable, but he can sleep without shivering and is not in danger of hypothermia. This rating is targeted at warm sleepers, typically men, as they tend to feel warmer in the same bag as the "average woman."
The extreme rating is the lowest temperature threshold provided by the ISO test. It indicates the temperature at which the bag can provide warmth and protection from extreme cold. This rating is important for users who plan to use the sleeping bag in extremely cold environments.
It is important to note that lab-tested temperature ratings may not always match real-world comfort levels due to various factors that a lab cannot simulate, such as differences in clothing, gear, body types, weather conditions, and individual variations in internal heat generation. Therefore, it is recommended to use the ISO test as a guide and consider other factors when choosing a sleeping bag for specific needs and preferences.
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Consider the type of insulation used
Sleeping bags can be insulated with either down or synthetic materials. Down refers to animal feathers, most commonly goose or duck. Higher-quality down has a greater ability to stick together in a single mass, a factor known as 'cling'. Synthetic insulation, on the other hand, is typically made of polyester fibres, which resemble cotton candy. Branded synthetics, such as Thermolite®, tend to retain their loft for longer than generic synthetics.
The type of insulation used will affect the bag's warmth-to-weight ratio, compressibility, water resistance, maintenance requirements, and price. Down bags generally have a higher warmth-to-weight ratio and are lighter than synthetic bags of a comparable temperature rating. They are also more compressible, making them easier to pack into a smaller volume. However, down loses its insulating properties to a greater degree when wet, so synthetic insulation may be preferable in humid or wet climates.
Down bags are typically more expensive and require more careful maintenance than synthetic bags. Down bags should not be stored compressed for extended periods, as they will lose their loft or insulating properties. Synthetic bags, on the other hand, can be stored compressed for longer periods but should not be permanently stored in this state. They require less maintenance and are generally heavier and bulkier than down bags of comparable warmth.
It's worth noting that the construction method of the sleeping bag also plays a crucial role in its performance. The insulation in the bag, combined with its construction, provides the necessary airspace or loft to minimise heat loss. Well-constructed bags with poor insulation or poorly constructed bags with excellent insulation may not perform satisfactorily.
When choosing a sleeping bag, it's essential to consider the intended use and your budget. If you prioritise a lightweight bag and are willing to invest more, a down bag could be the best option. However, if you anticipate using the bag in humid or wet conditions, synthetic insulation may be a wiser choice. Additionally, consider the bag's construction, temperature rating, and your personal preferences for comfort.
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Frequently asked questions
If you can't find any information on the temperature rating of your old sleeping bag, you can make a rough guess by measuring how much loft it has been able to retain over the years.
Temperature ratings are estimates based on lab testing. The ISO test involves placing a heavily instrumented electronic mannequin, dressed in long underwear, inside the sleeping bag, and positioning it on top of 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.
Sleeping bags are assigned temperature ratings based on the ISO test, which provides three temperature thresholds: a comfort rating, a limit rating, and an extreme rating. If you tend to sleep cold, pay attention to the comfort rating. If you tend to sleep warm, consider the lower limit rating.
You can improve the temperature rating of your sleeping bag by adding a sleeping bag liner or a properly insulated sleeping pad.
