Colin Snow
Sleeping bag temperature ratings are based on standardised testing, which involves placing a thermal mannequin, dressed in long underwear or standard pyjamas, inside the sleeping bag, and positioning it 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. This standardised testing provides three temperature thresholds: a comfort rating, a limit rating, and an extreme rating. However, it's important to note that these ratings are estimates, and real-world comfort may differ due to various factors such as clothing, body type, and weather conditions. Therefore, when choosing a sleeping bag, it's recommended to consider a variety of factors, such as the expected nighttime temperatures, the fit of the bag, and whether you tend to sleep hot or cold.
| Characteristics | Values |
|---|---|
| Standardised Testing | ISO Test |
| Temperature Thresholds | Comfort rating, Limit rating, Extreme rating |
| Lab Testing | A sleeping pad is placed under the bag, and a test dummy inside the bag is dressed in base layers |
| Numbers on Bag Names | The brand will round up or down to a number that ends in a 0 or a 5 |
| Comfort Rating | Based on the air temperature at which the "average female" can sleep comfortably through the night |
| Limit Rating | Based on the temperature at which the "average man" can maintain his thermal equilibrium in a curled-up position |
| Extreme Rating | 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 |
| ISO 23537 | The best rating system for sleeping bags |
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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 based on the temperature at which the "average woman" 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; he won't necessarily be comfortable at this temperature, but he won't be shivering and will be safe from hypothermia. The extreme rating is for emergency scenarios, indicating the minimum temperature a person can survive in the sleeping bag for up to six hours.
It's important to note that these ratings are not set in stone and can vary depending on individual factors. For example, if you tend to sleep cold, you may want to choose a bag with a higher comfort rating. Additionally, the bag's fit can also affect its warmth, so it's important to try it out before purchasing.
When choosing a sleeping bag, it's always a good idea to check the weather forecast and leave a safe margin between the expected nighttime lows and your bag's rating. It's also worth considering other factors that can affect your warmth, such as the R-value of your sleeping pad and the use of additional layers or blankets.
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Lab testing methods
The temperature rating of a sleeping bag is determined through standardised laboratory tests. The current ISO 23537 test is recognised globally, with the standard itself undergoing regular reviews. This test builds on the previous standard, EN 13537, which was introduced in 2005 to ensure that consumers could make like-for-like comparisons between sleeping bags.
The test protocol involves placing a test dummy, dressed in base layers, inside the sleeping bag, which is placed on a sleeping pad. The dummy is fitted with temperature sensors to represent a sleeping person. As the ambient temperature drops, measurements are recorded via the sensors. The data collected is then used to calculate a variety of comfort factors and heat ranges.
The test produces three temperature ratings: comfort temperature, limit temperature, and extreme temperature. 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.
It is important to note that temperature ratings are estimates and not absolute values. The lab tests cannot account for variations such as differences in people's clothing, gear, body types, weather conditions, and food intake. Therefore, the comfort level of a sleeping bag in the outdoors may differ from its tested temperature rating.
Additionally, not every sleeping bag has an ISO (or EN) rating. The test standard is not valid for bags designed for extreme cold or children's bags. Brands might also choose to forgo ISO testing for bags intended for mild conditions or casual use. In such cases, the temperature rating reflected on the bag is likely the brand's estimate rather than a standardised test result.
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Gender-specific ratings
When it comes to sleeping bags, the temperature rating is an important factor to consider, as it indicates the range of temperatures in which the bag is designed to provide comfort and protection. One aspect that influences the temperature rating is whether the sleeping bag is designed with a gender-specific focus, taking into account the different physiological needs of men and women.
Men and women differ in terms of their average height and weight, and these physical differences can affect how they experience temperature. On average, women tend to have a lower basal metabolic rate compared to men, which means they produce less internal body heat. As a result, women may feel colder more quickly and require a sleeping bag with a slightly higher temperature rating to stay comfortable. Conversely, men might opt for a bag with a lower temperature rating to accommodate their typically higher body temperature.
Gender-specific sleeping bags are designed to
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The importance of a sleeping pad
When it comes to camping gear, a good sleeping pad is just as important as a sleeping bag. Sleeping pads are what stand between you and the cold, hard ground, providing insulation and warmth. They are a crucial part of your sleep system, which consists of the sleeping bag, the sleeping pad, and the sleeper's clothing.
A sleeping pad's ability to insulate the sleeper from the ground is known as its R-value. The higher the R-value, the warmer the pad. For example, the Therm-a-Rest Neoair Xtherm has an R-value of 5.7, making it one of the best-insulating pads available, suitable for use in temperatures as low as -40° Celsius. Some sleeping pads also feature heat-reflective materials, which direct body heat back towards the sleeper.
When choosing a sleeping pad, it's important to consider factors such as length, width, shape, weight, cushioning, ease of inflation, durability, and cost. For example, if you're a broader person or feel like you need more space to move around at night, you might opt for a wider or rectangular-shaped pad. If you're backpacking, you might prioritize weight, durability, and packed size over other factors. On the other hand, if you're car camping, you might prefer a thicker, more luxurious pad that provides more comfort.
Self-inflating pads, like the Therm-a-Rest LuxuryMap Sleeping Pad, offer a combination of open-cell foam insulation and air. They are comfortable, reasonably compact, and provide excellent insulation. They can also be adjusted for firmness by adding or releasing air. However, they tend to be heavier and more expensive than simple foam pads and are not as compact as air pads. Air pads, on the other hand, are lightweight and come in a variety of styles, including lightweight options for backpacking and extra-thick, warm options for glamping.
Ultimately, the right sleeping pad for you will depend on your specific needs and preferences. It's always a good idea to try out different pads in person to find the one that provides the best combination of comfort, warmth, and convenience for your camping trips.
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Limitations of the rating system
The standardized testing used to assign temperature ratings to sleeping bags (the ISO Test) provides three temperature thresholds: a comfort rating, a limit rating, and an extreme rating. However, the names can be misleading as sleep comfort is a personal preference, and whether you sleep warm or cold at night determines how much insulation you need in your bag. The ratings are estimates, and while lab testing simulates how a sleeping bag should be used, it cannot account for all variables. For example, differences in people's clothing and gear, body types (warm and cold sleepers), changing weather conditions, and food intake can all affect how warm a person feels in a sleeping bag.
Additionally, not all sleeping bags have an ISO (or EN) rating. The test standard isn't valid for bags designed for extreme cold or children's bags. The ISO test is based on the assumption that the ""average woman" will feel colder in the same bag as the "average man," which may not always be the case. The comfort rating, which is the temperature for colder sleepers, is typically used for women's bags, resulting in women's bags weighing more than men's bags at a given temperature.
The numbers on bag names may not always match the exact temperature ratings. For simplicity, brands may round up or down to a number that ends in 0 or 5, and there are no rules for rounding. The EN and ISO tests use a heated mannequin dressed in base layers and placed on a sleeping pad inside a cold chamber to simulate sleeping conditions. However, this may not accurately represent real-world conditions, and the comfort level of a sleeping bag in the outdoors may differ from its tested temperature rating.
Finally, the rating system does not account for individual preferences or needs. Some people may prefer a warmer or cooler sleeping environment, and the rating system only provides a general guide. It is important to consider your own internal thermostat and choose a bag with a comfort rating that matches your needs. Additionally, the rating system may not be suitable for all outdoor sleeping situations, such as wild camping in mountainous areas where temperatures can drop significantly.
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Frequently asked questions
The three standard sleeping bag temperature ratings are the Comfort rating, the Limit rating, and the Extreme rating.
The Comfort rating is the temperature at which the "average woman" can sleep comfortably through the night without curling up for warmth.
The Limit rating is the temperature at which the "average man" can sleep for eight hours in a curled-up position without waking.
The Extreme rating is the minimum temperature at which a person can remain in the sleeping bag for up to six hours without risking hypothermia.
A thermal mannequin, wearing standardised clothing, is placed inside the sleeping bag, which is then subjected to decreasing air temperatures. The amount of electrical energy needed to maintain the mannequin's initial temperature is measured, and the results are correlated to real-world outcomes.
