Ashwin Lewis
When choosing a sleeping bag, the key factor to consider is its temperature rating. This is because the temperature rating indicates the range of temperatures for which a sleeping bag is suitable. Sleeping bags with a 15-degree rating are designed to keep the average sleeper warm and toasty unless the air temperature drops below 15 degrees. However, it's important to note that temperature ratings are estimates and not exact gospel. This is because they don't account for individual differences in body types, metabolic rates, clothing, gear, and sleeping pads. Additionally, the age of a sleeping bag can impact its warmth, as older bags may lose their loft and down over time. Therefore, it's recommended to use temperature ratings as a guide and consider other factors when choosing a sleeping bag for your specific needs.
| Characteristics | Values |
|---|---|
| Meaning | A 15-degree sleeping bag is designed to keep the average sleeper warm and comfortable at temperatures down to 15 degrees. |
| Temperature ratings | Temperature ratings are estimates and are not precise. The actual temperature a bag can withstand may vary. |
| Lab testing | Lab testing uses a mannequin with temperature sensors dressed in a base layer, socks, and a hat, placed on a sleeping mat inside a cold chamber. |
| Variables | Variables such as clothing, gear, body type, weather, and food can affect the comfort level of a sleeping bag. |
| EN and ISO ratings | EN and ISO ratings provide temperature ranges and limits to compare sleeping bags from different brands. |
| Comfort rating | The comfort rating is the temperature at which the average person should feel comfortable. It is typically 10-20 degrees higher than the lower limit. |
| Lower limit | The lower limit is the coldest temperature at which a man will likely feel comfortable. |
| Unisex bags | Unisex bags rated for 15 degrees may only be comfortable for women down to 27 degrees due to physiological differences. |
| Women's bags | Women's bags are usually bigger and heavier than men's bags to provide the same temperature rating due to the need for more insulation. |
| Season rating | A four-season sleeping bag is designed for winter use, while a five-season bag is for expedition or high-altitude use in extremely cold temperatures. |
| Backpacking | For backpacking, consider a bag with a higher warmth rating if hiking in frosty conditions or at elevation. |
| Age of the bag | Older sleeping bags may lose loft and down insulation, affecting their temperature rating over time. |
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What You'll Learn
Sleeping bag temperature ratings are estimates
Sleeping bag temperature ratings are a complicated topic. While they provide a useful estimate of how warm a sleeping bag will be, they are not always accurate.
Firstly, it is important to understand how sleeping bags are tested for warmth. Lab-tested temperature ratings, indicated by ""EN" or "ISO" ratings, involve placing a heated mannequin with 15 temperature sensors (to represent a sleeping person) inside the bag. The mannequin is dressed in a base layer, tights, long socks, and a hat, and placed on a closed-cell foam sleeping mat inside a cold chamber. As the temperature drops, measurements are recorded via the sensors on the mannequin, and these results are used to calculate the EN or ISO temperature ranges and limits. This protocol ensures consistency across sleeping bag tests, but it does not account for all variables.
For example, the mannequin is assumed to be using a sleeping pad with an R-value of approximately 5.5. However, if you use a pad with a lower R-value, your bag may not feel as warm as the stated limits. Additionally, the mannequin is dressed in specific clothing, but in reality, people may wear different types and layers of clothing, which can affect their warmth. Other factors that can impact warmth include body type (some people naturally feel warmer or colder), metabolism, food intake, and changing weather conditions.
The age and care of your sleeping bag can also affect its warmth. Over time, a sleeping bag may lose its loft and down filling, resulting in decreased warmth. Storing your bag open instead of stuffed can help maintain its condition.
Furthermore, not all manufacturers use the same rating system. Some companies, like Big Agnes, use their own independent rating system, which has not been third-party certified. Marmot, on the other hand, only publishes one temperature, which customers must assume is the lower limit.
When choosing a sleeping bag, it is recommended to consider the lowest expected temperature you will encounter and subtract 10 degrees to be safe. It is also important to know your personal internal thermostat—do you tend to feel cold or hot? If you often feel cold, opt for a bag with a comfort rating that is significantly lower than the coldest expected temperature. If you sleep warm, you may rely on lower-limit ratings, but still allow for a buffer of a few degrees Celsius.
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The lowest temperature a 15-degree bag will keep you warm
Firstly, the temperature ratings are based on lab testing that may not account for all real-world variables. For example, factors such as clothing, gear, body type, weather conditions, and individual metabolism can all impact how warm you feel in a sleeping bag. Additionally, the shape and features of the sleeping bag itself can also affect its warmth, with roomier bags tending to sleep colder than their ratings.
Another important consideration is the age of the sleeping bag. Over time, a sleeping bag can lose its loft and down filling, which can reduce its insulating properties. A 10-year-old 15-degree bag, for example, may end up offering closer to a 30-degree level of warmth.
It's also worth noting that the comfort ratings on sleeping bags are typically based on the average sleeper, and individual factors such as gender, body mass, and circulation can affect how warm you feel in a bag. Women's sleeping bags, for instance, tend to have higher comfort ratings because the average woman feels colder in a sleeping bag than the average man.
Therefore, when choosing a sleeping bag, it's generally recommended to consider the lowest expected temperature and subtract 10 degrees to be safe. For example, if you're expecting temperatures around freezing, a 15-degree bag should be suitable. However, if you tend to sleep warm, you may be comfortable with a higher-rated bag, while cold sleepers may need a bag with a lower temperature rating.
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Lab testing simulates how a sleeping bag is used
A 15-degree sleeping bag is intended to keep its user warm and comfortable at temperatures down to 15 degrees, assuming the sleeper is wearing long clothes and using a sleeping pad. However, lab testing simulates how a sleeping bag should be used, and these tests cannot account for all variables.
Lab-tested temperature ratings, indicated by "EN" or "ISO" ratings, are useful for comparing sleeping bags from different brands. The standardised tests involve placing a sleeping pad under the bag and a test dummy inside the bag dressed in base layers. While this ensures all tests are done the same way, it cannot account for variations such as differences in clothing, gear, body types, weather conditions, and food intake. For example, a bag's temperature rating may not account for an individual's metabolic rate, gender, or age.
In addition to lab testing, some companies also test their sleeping bags in campgrounds or their own backyards. These tests involve sleeping in the bags each night and rating them on comfort. Testers may also examine each bag's unique features, such as shoulder baffles, drawstrings, and full-length zipper draft tubes, which can help maximise body heat.
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EN and ISO ratings systems
A 15-degree sleeping bag is intended to keep the average sleeper warm and comfortable unless the air temperature drops below 15 degrees. These specifications assume that the sleeper is wearing long clothes and using a sleeping pad underneath. However, it's important to remember that factors like age, gender, metabolic rate, and other variables can affect an individual's comfort level.
Now, let's delve into the EN and ISO ratings systems for sleeping bags:
EN Ratings:
The EN rating, short for "European Norm", was the original standard adopted by the sleeping bag industry. It provided a consistent but imperfect way to measure and report temperature ratings. EN ratings are still commonly used and referenced by backpackers and retailers. The EN rating system involves standardised laboratory tests that produce a rating range for each sleeping bag. Two specific temperature ratings within this range are:
- Comfort Rating: Indicates the temperature at which a cold sleeper might feel comfortable. This is typically used for women's bags as women tend to feel colder than men at the same temperature.
- Lower Limit Rating: Indicates a lower temperature at which a warm sleeper might still feel comfortable. This is typically used for men's bags.
ISO Ratings:
The ISO rating system is overseen by the International Standards Organization (ISO). The ISO testing method is almost identical to the EN bag test, allowing for easy comparison between old EN-rated bags and newer ISO-rated bags. ISO 23537, published in 2016, replaced the European Norm 13537 standard to make temperature ratings more consistent. ISO ratings are less commonly seen on sleeping bags, but they provide valuable information. Like the EN ratings, ISO ratings are based on standardised laboratory tests that consider various factors, including:
- Sleeping pad: A sleeping pad is placed under the bag during testing.
- Clothing: The test dummy is dressed in base layers to simulate real-world conditions.
- Body type: The tests account for variations in body types, recognising that different people run at different temperatures.
- Environmental factors: ISO ratings consider external factors such as wind and humidity, which can affect overall warmth.
In summary, while the EN and ISO ratings systems provide a great baseline for choosing a sleeping bag, they are not absolute guarantees of comfort. Individual factors and real-world conditions will always vary, so it's essential to use these ratings as a guide and consider other variables when preparing for your outdoor adventures.
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The comfort rating is usually 10º-20º higher than the lower limit
Sleeping bag temperature ratings are a complex topic, and it's important to understand how these ratings are determined to make an informed purchase decision. When you see a "15-degree bag," it means that the bag is designed to keep the average sleeper warm and comfortable down to temperatures of 15 degrees. However, it's crucial to remember that these ratings are estimates and not absolute guarantees.
Now, let's delve into the concept of comfort ratings and their relationship to lower limits. The comfort rating of a sleeping bag refers to the temperature at which the bag is expected to keep a colder sleeper comfortable without the need for additional blankets. This rating is typically intended for women, as data has consistently shown that the average woman will feel colder than the average man in the same sleeping bag. The comfort rating is usually 10º-20º higher than the lower limit, meaning a unisex bag rated for 15º may only be comfortable for a woman down to 27º. This explains why a man might feel cozy in a 15-degree bag, while a woman might start feeling chilly at 35º or 40º in the same bag.
The difference in comfort ratings between genders is due to physiological differences, and it's important for manufacturers to consider these variations when designing sleeping bags. To achieve the same temperature rating, women's bags often require more insulation, making them bigger and heavier than the same model designed for men. This is why women's-specific bags from the same brand are usually larger and heavier than their men's counterparts.
It's worth noting that the temperature rating on a sleeping bag doesn't always indicate optimal performance. Instead, it represents the point at which the bag may start feeling too chilly for comfort. Additionally, these ratings are based on lab tests that use standardised protocols, such as placing a sleeping pad under the bag and dressing a test dummy in base layers. However, these tests cannot account for various factors, including differences in clothing, gear, body types, metabolism, and changing weather conditions.
When choosing a sleeping bag, it's recommended to consider the lowest expected temperature during your trip and then subtract 10 degrees to be safe. For example, if you're camping in an area where temperatures can dip to freezing, a bag with a 28°F ISO Comfort rating (16 °F Lower Limit) should suffice. It's also essential to consider your personal internal thermostat—if you tend to feel cold, opt for a bag with a lower comfort rating than the coldest expected temperature.
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Frequently asked questions
A 15-degree sleeping bag is designed to keep the average sleeper warm and comfortable in temperatures down to 15 degrees. This assumes that the sleeper is wearing long clothes and using a sleeping pad underneath.
The key factor when choosing a sleeping bag is its temperature rating. You should consider the lowest temperature you’re likely to encounter and your personal internal thermostat—whether you tend to feel cold or hot. If you often feel cold, opt for a bag with a comfort rating that is lower than the coldest expected temperature. If you sleep warm, you can rely on the lower-limit ratings.
The EN and ISO ratings are lab-tested temperature ratings that indicate the warmth of a sleeping bag. The EN 13537 offers four different temperature ratings: EN Upper Comfort, which is the highest temperature at which an average 70kg man should feel comfortable, and EN Comfort, which is the temperature at which an average 60kg woman can sleep comfortably through the night.
