Gina Johnson
Sleeping bag temperature ratings are a complex topic. The rating systems in place, such as EN (European Norm) and ISO (International Standards Organization), are designed to help consumers make informed decisions about their purchases. These ratings are determined through standardized laboratory tests, which involve placing a test dummy inside the bag and measuring the amount of electrical energy required to maintain its initial temperature as the air temperature is lowered. However, these ratings are only estimates, as they cannot account for individual differences in body types, clothing, gear, and environmental conditions. It's important to consider factors such as the lowest expected temperature, personal comfort preferences, and the insulating capacity of the sleeping pad when choosing a sleeping bag. Additionally, the shape and size of the mannequin used in the tests might not represent all body types, so trying out the sleeping bag for fit is recommended.
| Characteristics | Values |
|---|---|
| Standard | EN (European Norm) |
| Current standard | ISO (International Standards Organization) |
| Test method | A heavily instrumented electronic manikin, wearing long underwear, is placed inside the sleeping bag, which is positioned on a foam sleeping pad. The temperature of the air is then lowered, and the amount of electrical energy needed to maintain the manikin's temperature is measured. |
| Rating range | Two temperature ratings are specified: Comfort rating and Lower limit rating. |
| Comfort rating | Indicates the temperature at which a cold sleeper might feel comfortable. This is the rating used for women's bags. |
| Lower limit rating | Indicates the temperature at which a warm sleeper might still feel comfortable. This is the rating used for men's bags. |
| Factors affecting warmth | Insulation from the ground or sleeping surface, clothing, body weight, and food are some factors that can affect the warmth of the sleeper. |
| Season rating | One-season bags are for summer use, two-season bags are for spring, summer, and mild autumn nights, and three-season bags are for spring, summer, autumn, and temperatures just below freezing. |
| ISO standard | ISO 23537 |
| Temperature ratings | Comfort, Limit, and Extreme |
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What You'll Learn
Sleeping bag temperature ratings are estimates
The numbers on bag names are also not exact indicators of temperature ratings. For example, the Men's "Snugglebuggle" 15 Bag may actually have an ISO lower-limit rating of 18°F (Fahrenheit). Brands often round up or down to a number ending in 0 or 5 for simplicity, and there are no rules dictating their rounding methods.
It's important to note that sleeping bag ratings provide a baseline for comparison, but they cannot guarantee warmth down to a specific temperature due to individual variations. Factors such as body shape, size, age, metabolic rate, muscle mass, and personal internal thermostat influence how warm or cold one feels. Additionally, external factors like camping conditions, the fit of the sleeping bag, and the warmth of the sleeping mat also play a role in determining warmth.
The EN (European Norm) rating scale was the original standard for sleeping bag temperature ratings. Today, the ISO (International Standards Organization) oversees bag testing, using ISO 23537, a heated manikin system with multiple temperature sensors in a climate-controlled room. This test determines the power needed to maintain warmth in a cold room, indicating the bag's thermal resistance. However, ISO testing does not account for individual differences in internal heat generation.
When choosing a sleeping bag, it's recommended to consider the lowest anticipated temperature and your personal tolerance for cold. If you often feel cold, opt for comfort ratings and select a bag with a lower comfort figure than the coldest expected temperature. If you tend to sleep warm, you may rely on lower-limit ratings, but it's still advisable to allow a buffer of a few degrees Celsius.
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Lab testing methods
The EN and ISO tests use a heated mannequin with 15 temperature sensors to represent a sleeping person. The mannequin is dressed in a base layer 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. As the temperature drops, measurements are recorded via the sensors on the mannequin. The results are used to calculate the EN or ISO temperature ranges and limits.
The EN ISO 23537 standard is in place to help give baseline temperature measurements of sleeping bags across the industry. The EN ISO test produces a series of temperature limits, including comfort, limit of comfort, and extreme ratings. The comfort rating indicates the minimum temperature where an individual can sleep in a relaxed position and get a good night's sleep. The limit of comfort rating is the temperature range where an individual sleeping in a curled position and fighting against the cold can still sleep through the night. The extreme rating is for an emergency scenario – it is the minimum temperature a person can remain in the sleeping bag for up to six hours in a curled position while really fighting against the cold.
It is important to note that temperature ratings are estimates and not exact measurements. Lab testing simulates how a sleeping bag should be used, but it cannot account for variations such as differences in people's clothing, gear, body types, changing weather conditions, and more. Therefore, when using a sleeping bag outdoors, its comfort level may differ from its tested temperature rating.
The standardized testing used to assign temperature ratings to sleeping bags provides three temperature thresholds: comfort, limit, and extreme ratings. The comfort rating is based on the air temperature at which the "average female" can sleep comfortably through the night without feeling cold. The limit rating is based on the temperature at which the "average man" can maintain his thermal equilibrium in a curled-up position without feeling cold. The extreme rating indicates the temperature at which there is a risk of health damage to a "standard woman" by hypothermia.
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The importance of insulation
The quality of insulation in a sleeping bag is critical to its performance and your comfort. Better insulation will ensure the bag retains more heat, keeping you warmer. The type of insulation used in sleeping bags can vary, with down being a superior insulator to synthetic fillings, though it is often more expensive.
The insulating properties of a sleeping bag are also impacted by the bag's design. For example, the shape of the bag and the number of layers can affect its ability to retain heat. Mummy-shaped bags, for instance, are designed to be more form-fitting, reducing the amount of dead space that needs to be heated.
Additionally, it is important to consider the insulating properties of the sleeping surface. A sleeping bag's insulation is reduced by your body weight compressing the bag beneath you. Therefore, it is essential to use an insulated pad or air mattress to compensate for this loss of insulation. The R-value of the sleeping pad or mattress is an indication of its insulating capabilities, and choosing one with an appropriate R-value for the expected ground temperatures is crucial.
Finally, it is worth noting that the effectiveness of a sleeping bag's insulation can be influenced by external factors such as weather conditions, your diet, and your clothing. A well-insulated bag may still fail to keep you warm if it is wet, or if you are not wearing adequate clothing to retain body heat.
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How to compare sleeping bag ratings
Sleeping bag ratings are a complex and sometimes confusing topic. The ratings are estimates and are based on lab testing that simulates how a sleeping bag is used. A sleeping pad is placed under the bag, and a test dummy, dressed in base layers, is placed inside the bag. This is known as the ISO test, which is recognised globally and overseen by the International Standards Organization. The EN Rating scale, the original standard, was influenced by Mountain Equipment and is still used today, with the method almost identical to the ISO test.
The ISO test involves placing a heavily instrumented electronic manikin, 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 manikin’s initial temperature is measured. The test is repeated until equilibrium is reached, and the thermal resistance is converted into temperature ratings based on historical data. This standard produces three temperature ratings: comfort, limit, and extreme. The comfort temperature is where a "standard woman" with a relaxed posture is just not feeling cold. The limit temperature is where a "standard man" with a curled-up posture is just not feeling cold, and this is the number most retailers and brands refer to. The extreme temperature is where there is a risk of health damage to a "standard woman" by hypothermia.
When comparing sleeping bag ratings, it's important to consider the lowest temperature you’re likely to be sleeping in, as well as your own personal internal thermostat. If you often feel cold, use comfort ratings as a baseline and get a bag with a significantly lower comfort figure than the coldest expected temperature. If you sleep warm, you might be able to rely on lower limit ratings, but it's still recommended to give yourself a buffer of a few degrees Celsius. It's also worth noting that sleeping bag temperature ratings are based on lab tests that may not account for all variables, such as differences in people's clothing, gear, body types, and weather conditions. Therefore, the comfort level of a sleeping bag in real-world use may differ from its tested temperature rating.
In addition to temperature ratings, other factors can impact the warmth of a sleeping bag, such as the insulating sleeping pad and liner used, the type of clothing worn, and the fit of the sleeping bag. It's also important to consider the seasonality of the sleeping bag, as some bags are designed for specific seasons or a combination of seasons. For example, a three-season bag can be used throughout spring, summer, and autumn, while a one-season bag is designed for summer use only. When comparing sleeping bag ratings, it's crucial to consider all these factors to ensure you choose the right bag for your needs and preferences.
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Seasonality of sleeping bags
The seasonality of a sleeping bag is an important factor to consider when purchasing one. Sleeping bags are available in different seasonal ratings, which indicate the time of year and weather conditions in which they are most suitable for use.
The temperature ratings of sleeping bags are based on an "average sleeper" and are designed to provide a general guide to help consumers compare different bags. Lab testing is carried out to determine the temperature ratings, but it's important to remember that individual factors, such as clothing, metabolism, and sleeping pads, can also influence the comfort level of the sleeper.
When choosing a sleeping bag for a specific season, it's recommended to consider the expected temperatures during that time of year. For example, a 20° bag is versatile and suitable for spring and autumn shoulder seasons. In contrast, a bag with a temperature rating of 10° or lower is more appropriate for the coldest winter months.
The shape of the sleeping bag also plays a role in its seasonality. Rectangular bags offer more space to move around and can be unzipped for ventilation in warmer weather. On the other hand, mummy-shaped bags are snugger and designed to retain warmth more effectively, making them a better choice for colder seasons.
Additionally, the insulation type of the sleeping bag should be considered for different seasons. Down insulation is superior for colder seasons due to its excellent warmth-to-weight ratio, compressibility, and durability. Synthetic insulation may be more suitable for warmer seasons as it is often more affordable, but it may not provide the same level of warmth as down.
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Frequently asked questions
Sleeping bag ratings give a baseline for comparison. They are determined by lab tests that simulate how a sleeping bag is used. However, they are not a guarantee of how warm you will be in a sleeping bag, as there are many individual factors that affect this.
The most widely recognised testing standard is ISO 23537, which uses a heated mannequin with temperature sensors in a climate-controlled room. The mannequin is dressed in standard pyjamas or long underwear and measures the power needed to maintain warmth in a cold room.
First, you need to know the lowest temperature you’re likely to be sleeping in. Then, consider whether you generally feel hot or cold. If you feel cold, use the comfort rating as a baseline and get a bag with a lower comfort figure than the coldest expected temperature. If you feel hot, you might be able to rely on the lower limit rating.
The comfort rating indicates the temperature at which a cold sleeper might feel comfortable. This is the rating used for women's bags. The lower limit rating is always lower than the comfort rating and indicates the temperature at which a warm sleeper might still be comfortable. This is the rating used for men's bags.
