Herbie Murray
Sleeping bag ratings are a complex topic. The key factor when choosing a sleeping bag is its temperature rating, which indicates its warmth and suitability for different conditions. Sleeping bag temperature ratings are determined through standardised laboratory tests, which produce a rating range for each sleeping bag. The EN Rating scale, for example, produces a Lower rating for male sleepers and a Comfort rating for female sleepers. However, real-world comfort may differ from lab-tested temperature ratings due to various factors such as clothing, gear, body type, weather conditions, and food. Additionally, the same temperature rating may feel different across brands and individuals, making it essential to understand how the ratings work to choose the right sleeping bag for your needs.
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What You'll Learn
Sleeping bag temperature ratings
The EN Rating scale is a scientific test used to determine the warmth of a sleeping bag, producing a "Lower Limit" rating for male sleepers and a "Comfort" rating for female sleepers. The Comfort rating indicates the temperature at which a female sleeper can sleep comfortably through the night without feeling cold, while the Lower Limit rating indicates the temperature at which a male sleeper might still feel comfortable. These ratings are based on standardised laboratory tests overseen by the International Standards Organization (ISO). However, it's important to note that these ratings are estimates, and real-world comfort may differ due to various factors such as clothing, gear, body type, and weather conditions.
Sleeping bags are also categorised by season ratings, indicating their suitability for different times of the year. For example, "one-season" bags are designed for summer use, while "three-season" bags can be used throughout spring, summer, and autumn. "Four-season" bags are designed for winter use, optimised for cold conditions. Additionally, the term "five-season" is sometimes used for bags designed for expedition or high-altitude use in extremely cold temperatures.
When choosing a sleeping bag, it's recommended to consider your personal preferences and sleeping habits. If you tend to sleep cold, pay attention to the Comfort rating and consider adding 10 degrees to the rating for women or cold sleepers. It's also suggested to overshoot the expected temperature range to ensure warmth, especially in colder climates.
It's worth noting that temperature ratings are not standardised across all manufacturers, and there may be variations in testing methods and interpretations. Therefore, it's essential to consider multiple factors when selecting a sleeping bag, including fit, fabric, and insulation, to ensure a good night's sleep during your outdoor adventures.
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How are sleeping bags tested
Sleeping bags are tested in laboratories to determine their temperature ratings. The tests are designed to standardise the method for rating the warmth of sleeping bags. The EN (European Norm) and ISO (International Organization for Standardization) methods are broadly similar. They both involve using a heated mannequin wearing a long underwear top and bottom, a hat, and a closed-cell foam sleeping pad. The mannequin is placed inside the sleeping bag, which is then put in a cold chamber. As the temperature drops, measurements are taken via sensors on the mannequin to determine how much energy per given area is necessary to maintain standard skin temperature. This data is then used to calculate the temperature ranges and limits for the sleeping bag.
The EN and ISO methods offer different temperature ratings, but the most relevant ones are the "Comfort" and "Lower Limit" ratings. The Comfort rating is the temperature at which a cold sleeper might feel comfortable, and it is typically 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 feel comfortable. This rating is usually used for men's bags.
It is important to note that the lab-tested temperature ratings may not accurately reflect the real-world comfort of the sleeping bag. Variables such as differences in people's clothing, gear, body types, weather conditions, and food intake can affect the actual comfort level of the bag. Additionally, the mannequin used in the test does not move, which can create cold spots in the sleeping bag that would not be present in real-world use.
Some companies choose not to use the EN or ISO testing methods and instead set their own temperature ratings based on internal testing. For example, brands like Feathered Friends and Western Mountaineering are known for their non-EN/ISO-rated bags that are widely used by serious backpackers and alpinists.
When purchasing a sleeping bag, it is essential to consider your own personal preferences and internal thermostat. If you frequently feel cold, it is recommended to choose a bag with a lower comfort rating than the coldest expected temperature. If you tend to sleep warm, you may rely on the lower limit ratings, but it is still advisable to allow for a buffer of a few degrees Celsius.
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Differences between EN and ISO ratings
Sleeping bag temperature ratings are determined by lab-tested temperature ratings, as indicated by "EN" or "ISO" ratings. The EN (European Norm) standard was the original standard adopted by the sleeping bag industry. However, in April 2017, a new entity, the ISO (International Standards Organization), introduced updated standards for sleeping bag testing. The key differences between EN and ISO ratings are as follows:
EN Ratings
The EN 13537 standard was introduced in 2005 to ensure that consumers could directly compare sleeping bags with a given rating. This standard provided a way to determine how well an adult would stay warm as the air temperature dropped. The EN test procedure involves using a heated mannequin with 15 temperature sensors to represent a sleeping person. The mannequin is dressed in a base layer and placed inside the sleeping bag on top of a sleeping mat inside a cold chamber. The EN ratings provide four different temperature ratings: comfort, lower limit, extreme, and maximum temperatures.
ISO Ratings
The ISO 23537 standard was published in 2016 as an update to the EN standard to make it more consistent. The ISO standard gives three different temperature ranges: Comfort Range, Transition Range, and Extreme Range. The Comfort Range is defined as the temperature range where a standard woman feels "not cold" while sleeping in a relaxed posture. The Transition Range is where a standard man is fighting against the cold and is curled up inside the sleeping bag but is not shivering. The Extreme Range states that a strong sensation of cold is to be expected, and there is a risk of health damage by hypothermia. It is important to note that not all sleeping bags have an ISO rating, and those that do not specify a testing standard may not provide accurate temperature ratings.
Despite the differences in temperature ranges, the difference between EN and ISO ratings is not relevant for consumers. Both standards are used to determine the baseline performance level of a sleeping bag and provide a general idea of how the bag will perform in real-world conditions. The key ratings in both systems are the Comfort and Limit ratings, which indicate the likely performance limit of the sleeping bag.
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Seasonality and sleeping bag ratings
Sleeping bags are generally rated based on their temperature ratings, which indicate the level of warmth they provide. These ratings are assigned through standardised laboratory tests, such as the EN (European Norm) and ISO (International Standards Organization) tests. The EN rating is widely used for backpacking bags and indicates the lowest temperature at which the bag should be able to keep you warm enough for sleeping. However, it's important to note that real-world comfort may differ from lab-tested temperature ratings due to various factors, including clothing, gear, body type, and weather conditions.
Seasonality plays a crucial role in choosing the right sleeping bag. A sleeping bag's season rating indicates how many seasons it can be used across the year. For example, a 3-season bag is designed for use in spring, summer, and autumn, while a 4-season bag can be used year-round, including winter. The temperature ratings on sleeping bags are typically given in degrees Fahrenheit or Celsius and provide an estimate of the comfort level you can expect at certain temperatures.
When selecting a sleeping bag, it's essential to consider the anticipated temperatures during your trips. For camping in spring, summer, and early fall, a bag with a temperature rating above 35°F is generally recommended for warm weather. A 20°F bag is highly versatile and can handle shoulder-season conditions, making it suitable for most of the year. If you plan to camp in colder months, a 10°F bag or even a 0°F bag may be necessary for comfort.
It's worth noting that sleeping bags for women often have more insulation, making them warmer than similarly rated men's bags. This is based on the premise that women tend to sleep colder than men. Therefore, when choosing a sleeping bag, it's important to pay attention to the comfort rating, which indicates the temperature at which the average woman can sleep comfortably. Additionally, individual differences in body temperature regulation can impact the perceived warmth of a sleeping bag, so it's always a good idea to test your sleeping bag before relying on it in extreme conditions.
In summary, when selecting a sleeping bag, consider the seasonality and temperature ratings, and don't forget to account for individual preferences and comfort levels. Choosing the right sleeping bag can ensure a good night's rest during your outdoor adventures.
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How to choose the right sleeping bag
A good sleeping bag is essential for a good night's sleep outdoors. Here are some tips on how to choose the right one:
Temperature Rating
The temperature rating of a sleeping bag is a key factor in determining its suitability for your needs. Sleeping bags are typically rated based on the minimum temperature at which the average sleeper would be comfortable. For example, a bag rated 20°F is designed for an average sleeper down to 20 degrees Fahrenheit. It's important to note that these ratings are estimates and may not reflect your personal comfort level due to various factors such as clothing, gear, body type, and weather conditions. It is generally recommended to choose a bag with a lower temperature rating than you expect to encounter, especially if you tend to sleep cold.
Shape
The shape of your sleeping bag should align with your camping style and sleeping preferences. There are three basic shapes: Mummy, Rectangular, and Semi-Rectangular. Mummy bags are the most popular as they have a snug fit, making them warm and lightweight, ideal for backpacking. However, they may feel restrictive. Rectangular bags offer more room but are less efficient at heating. Semi-rectangular bags provide a balance between warmth and space.
Fit
The right fit is crucial for comfort and warmth. The bag should be long enough to accommodate your height, with a few extra inches to allow for spine decompression and body spread when lying flat. A bag that is too tight can compress the insulation, creating cold spots, while a bag that is too loose can result in excess space that requires more energy to heat. It is recommended to try the bag before purchase to ensure a comfortable fit.
Additional Features
Consider the placement of zippers, especially if you're left-handed. Zippers with guards or covers can prevent snagging. Fabric strength is important if you plan to use the bag in rugged conditions. Some fabrics have DWR treatment for damp conditions. Pockets and zipper coupling can also be useful features.
Sleep System
Don't forget to consider your sleep system as a whole. Combine your sleeping bag with appropriate accessories such as a sleeping pad, liner, and pillow to enhance your comfort and protection from heat loss.
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Frequently asked questions
Sleeping bag ratings are determined by their warmth and suitability for different conditions. The key factor is the temperature rating, which is based on how the bags are tested for warmth in a lab.
The three main temperature ratings are comfort, limit, and extreme. The comfort rating indicates the temperature at which a cold sleeper might feel comfortable. The limit temperature is where a "standard man" with a curled-up posture is just not feeling cold. The extreme rating gives an idea of how cold the air could be before there's a serious risk of hypothermia.
When choosing a sleeping bag, consider the seasonality of the bag, the temperature ratings, and your personal preferences. A one-season bag is designed for summer use, while a three-season bag can be used throughout spring, summer, and autumn. If you sleep cold, opt for a warmer bag with a higher comfort rating.
Real-world comfort may differ from lab-tested temperature ratings due to variations in people's clothing, gear, body types, weather conditions, and other factors. The EN rating scale, which is voluntary in the EU, may not represent your size, so it's important to try a sleeping bag for fit. The ISO 23537 test, considered the best rating system, has limitations in simulating airflow and the impact of face fabrics.
