To choose a sleeping bag, you can use our general catalog, which offers a convenient filter for sorting models by temperature parameters. However, before delving into that, let's explore the definitions of t ° comfort and limit. We will also discuss why these values are referred to as both male and female comfort ratings, as well as the purpose of extreme t ° and max (or Upper Limit) provided for sleeping bags. All of these topics will be covered in detail in this material.

Why are the temperature ratings of a sleeping bag important?

A sleeping bag offers various criteria for providing a comfortable sleep for tourists. These include its shape, width dimensions, and additional features such as a pillow compartment. However, the fundamental aspect of a comfortable overnight experience in nature is warmth. It is essential to prevent a sense of chilliness, cold limbs and discomfort. Without adequate warmth, tourists may experience interrupted sleep and frequent awakenings, hindering their ability to rest effectively.

The thermal performance of a sleeping bag is important not only for comfort, but also for the safety of the user. Due to the cold, hypothermia is possible, which poses a threat to health and even human life.

Choosing a sleeping bag based solely on seasonality is not always straightforward. One-season options are quite rare and manufacturers may have their own criteria for categorizing their products. Additionally, even during the summer, unexpected cold spells can occur. Therefore, it is important to have more specific information, such as clear temperature ranges, to determine the suitable usage of a sleeping bag.

The sleeping bag should prevent the user from feeling cold in winter, off-season and in summer.

Other criteria, of course, are also important, but in conjunction with temperatures. Therefore, we still advise you to read the material "How to choose a sleeping bag: the main rules and recommendations".

Demi-season sleeping bags

EN 13537 standard and basic temperature specs

The EN 13537 standard, introduced in 2002 and enforced in 2005, has significantly simplified the process of comparing sleeping bags based on their operating temperatures. This standard unified temperature specs across most manufacturers, replacing the previously diverse branded tests with different variables. Now, there is a single testing method, making it easier for buyers to make informed decisions.

Note that the first edition of the EN 13537 standard has subsequently been revised. Its latest version dates back to 2012 (EN 13537:2012), and adopted by most European countries. Subsequently, the new ISO EN 23537:2016 standard emerged, serving as the successor to EN 13537. It applies to a broader range of countries worldwide, including the United States of America, as members of the International Organization for Standardization (ISO). Furthermore, EN 23537 not only specifies thermal requirements but also includes guidelines for the fabrics and materials used in sleeping bags.

The design of temperature charts and scales may vary, but their fundamental content remains the same.

The EN 13537 standard has firmly established itself in the vocabulary of tourists, and it is still commonly referenced today, rather than its current successor, ISO EN 23537. Furthermore, many available sleeping bag models still have the old markings. However, when it comes to temperature specs, there are no significant differences between the standards.

Summer sleeping bags

What do the temperature values of the standard mean?

Both EN 13537 and ISO EN 23537 require the designation of three or four temperature parameters for a sleeping bag, namely:

  • max t° (the designation Upper Limit or maximum comfort temperature is also found);
  • comfort t° (Comfort, moreover, often referred to as t° comfort ♀, that is an acceptable temperature for women);
  • comfort limit t° (Lower Limit, simply Limit, or comfort t° ♂, that is an acceptable temperature for men);
  • extreme t° (Extreme or temperature zone of survival).

According to the standard, the last three values must be indicated. However, brands may choose not to designate the max temperature as it is not crucial for safety. This temperature mainly relates to discomfort caused by excessive heat and sweating. Users can address this issue by opening the zipper, using the sleeping bag as a blanket, or opting not to use it at all.

Sleeping bags often display temperature values in both Celsius and Fahrenheit, often including 6 values instead of 3.

The absence of a maximum temperature value does not imply non-compliance with the EN 13537 or 23537 standard for sleeping bags. Brands often choose to omit this value as an option, in part to avoid limiting the potential applications of their products.

The temperature values indicated for sleeping bags must necessarily take into account the following initial data:

  • the tourist spends the night in a tent;
  • under the sleeping bag there is a rug;
  • the sleeper is in socks and thermal underwear;
  • there are clear criteria for an "average" man and woman. The age of these tourists is the same — 25 years. The man is 173 cm tall and weighs 73 kg, while the woman is 160 cm and 60 kg respectively.

Considering this information, let's examine the meaning of temperature ratings using a specific example. You come across a sleeping bag labeled with the following symbols:

The temperature ratings are indicated on the official website, on the sleeping bag itself, on the label, and on the transportation case.

What do they mean:

  • t ° max is +23 ° C. This means that under this temperature, an "average" man can sleep comfortably for up to 8 hours in a relaxed position without excessive sweating. The sleeping bag can be partially opened, allowing the user to have their hands outside if desired.;
  • t° comfort ♀ is +10 °C. In a fully zipped sleeping bag and a hood(if any), at a temperature not lower than the indicated value, the “average” woman will be able to sleep n a relaxed position for at least 8 hours without waking up due to feeling chilly or cold;
  • t° comfort ♂ (t° limit) — +5 °C. In a fully zipped sleeping bag, an “average” man will be able to sleep from 8 hours in the fetal position, without feeling cold at an air temperature of at least +5 °C;
  • t° extreme is -9 °C. When the temperature drops to this value, the "average" woman will not freeze for up to 6 hours, provided she is curled up. Sleep will not be comfortable, hypothermia is also possible, but without the risk of death. In addition, this temperature will be relevant only when the user is not wet, hungry, tired or cold before the start of the rest.
Winter sleeping bags

What temperature ranges should be consider when selecting a sleeping bag?

When choosing a sleeping bag, beginners, female users, and those who are more sensitive to the cold should prioritize the comfort temperature (t ° comfort ♀ or t ° comfort). It is permissible for men and experienced tourists to focus on t° comfort ♂ or t° limit, as well as the range between this and the given “female” value.

First of all, you should pay attention to t° max when you are going to hike in the hot season with hot nights. But the comfort indicator also remains important in case of unexpected cold weather.

It is impossible to focus on t ° extreme. While some manufacturers may promote their sleeping bags as capable of withstanding temperatures as low as -9 °C, this primarily pertains to survival situations rather than ensuring a comfortable overnight stay. The extreme temperature rating serves as an indicator for potential emergencies and can be kept in mind to avoid panic in such situations.

How are sleeping bags tested for compliance with standards?

Tests according to EN 13537/23537 are carried out by independent specialized organizations, including the Norwegian Thelma AS, the German Hohenstein Institute, the American Institute for Environmental Research, etc. Checking the temperature specs is carried out indoors — in climatic chambers. Only new, dry sleeping bags are tested.

EN 13537 testing uses dummies, not human beings.

During testing, dummies equipped with thermocouples and surface sensors are used to simulate heat release from the human body. The test involves heating the dummy to 34 °C and measuring the thermal energy required to maintain this temperature across different parts of the dummy within a 30-minute period. The thermal resistance of the model is calculated based on the temperature difference on the surface of the “subject” and outside the sleeping bag (in the climate chamber).

Sleeping bags from +6 to +10 °C

Pros and cons of EN 13537/23537 standards

The main benefits of implementing EN 13537/23537 for buyers include:

  • the ability to more specifically compare sleeping bags from different manufacturers;
  • providing a clear view of the operating temperatures of the models;
  • the presence of indicators that apply to both men and women, although women, due to physiological differences, tend to feel colder faster;
  • an additional confidence factor in a sleeping bag if it has been tested according to EN 13537/23537.

There are also some downsides:

  • standards do not apply to children's sleeping bags, double and army (there are requirements in different countries) models, some versions for extreme conditions (at temperatures below -20 °C);
  • not all important factors are taken into account. In addition to gender, tourists may differ in age, weight, height, level of physical fitness, etc. (all previous tests were even less representative);
  • manufacturers have no legal obligation to comply with the requirements of EN 13537 or EN 23537;
  • the costs associated with conducting tests are ultimately reflected in the pricing of the finished product by the brands;
  • falsification of test results by unscrupulous trademarks is not ruled out.
EN 13537 and ISO EN 23537 do not apply to children, so their thermal conditions can first of all be checked empirically.

Let's talk in more detail about how to minimize the risks of cheating with data on the temperature ratings of sleeping bags.

Thermal confidence factors

While the EN 23537 standard is widely accepted globally, it is important to note that compliance with its requirements is not mandatory for sleeping bag manufacturers. It remains a recommendation rather than a compulsory standard. Consequently, some brands may employ tactics or even manipulate information to cater to consumer preferences.

The first interesting point is the subtleties of the wording. On the official website, on the sleeping bag, on its compression bag, the designation EN 13537 or EN 23537 may simply be mentioned, and there may be no temperature conditions. And it does not mean testing. Both noname brands and reputable brands that produce high-quality sleeping bags and perform their own measurements can increase the credibility of their products.

You may come across phrases like "temperatures tested in accordance with EN 23537" or "temperatures rated in accordance with EN 23537". The former indicates that an independent test was conducted, while the latter implies that the manufacturer conducted their own tests and calculations. It's important to note that the latter option is not necessarily inferior, as it depends on the brand's integrity and reputation.

The manufacturer can test the sleeping bag and slightly change the wording of compliance with the standard.

What factors of trust or distrust are there in addition to the fame (image) of the manufacturer? Here are some of them:

  • little difference between t° comfort and t° limit. The ideal temperature range for both men and women should be around 3 to 8 degrees Celsius. A larger difference of 10 degrees or more could indicate potential issues with testing or artificially lowered comfort limit indicators;
  • the type of insulation used in a sleeping bag is directly related to its temperature capabilities. Models designed for colder conditions often have natural down insulation or multiple layers of dense synthetic materials;
  • The weight of a sleeping bag is directly related to its temperature capabilities. Down-filled models are generally lighter than synthetic ones. A freezing-ready synthetic sleeping bag usually weighs around 2 kg or more, while a down-filled sleeping bag typically weighs around 1.2 — 1.5 kg. Comparing the weight of a sleeping bag from a reputable brand can provide a basis for analyzing products from newer brands and verifying their temperature specs.
Down sleeping bags

What else affects a comfortable overnight stay besides the temperature conditions of the sleeping bag?

The standardization of testing does not allow taking into account all the factors that somehow affect the thermal insulation of a sleeping bag and the sensations of a tourist during a night's rest. In general, according to EN 13537/23537, deviations of 5% from the specified temperatures are allowed. But in practice, the errors can be even greater, including due to:

  • various external factors — the level of air humidity, wind speed, etc.;
  • condition of the sleeping bag and its insulation. The key criterion for good thermal insulation is the dryness of the product. When a sleeping bag gets wet, heat loss can significantly increase. Additionally, the operational properties of the sleeping bag tend to deteriorate with each subsequent use;
In order for the temperature ratings of the sleeping bag to _work_, it needs to be dry.
  • individual sensitivity to cold. In general, there is a tendency for women and children to feel the cold more quickly than men. However, even within both genders, there can be significant variation in individual resistance to low temperatures;
  • body weight and height of the user. The bigger the tourist, the more heat they are given off and the longer it can stay inside the sleeping bag, preventing freezing;
  • age and fitness. Sports young people cope better with the cold, and children and the elderly are worse. They have less body heat. More experienced trekkers tend to be more tolerant of low temperatures than beginners;
  • operational properties of the used tourist rug. When choosing a model with a high coefficient of thermal conductivity (R-Value above 5), you can significantly reduce heat loss from the soil and increase the comfort of an overnight stay in frosty weather;
An important criterion for a warm overnight stay on a hike is a good rug under the sleeping bag.
  • clothing used. The test assumes the presence of thermal underwear and socks. A tourist can sleep both in ordinary underwear and adhering to the principle of layering to increase thermal insulation.

Fatigue, dehydration, and hunger can accelerate the onset of cold sensations in hikers. Additionally, individuals are sensitive to localized sensations of cold, such as freezing toes, hands, or drafts around the neck. It's important to note that the EN 13537 and EN 23537 standards cannot guarantee the complete absence of localized cooling.

Recommendations for choosing a sleeping bag for different weather and hiking conditions:

  • For hot summer, it is worth considering buying sleeping bags for which t° max is indicated. So it will be possible to choose a model and not experience discomfort from the heat (do not sweat during sleep).
  • From June to August, the night air temperature in our flat area rarely drops below +9 — +11 ° C, which can be considered a guideline for the temperature regime of the summer model.
  • For a hike in the off-season (for example, in mid-autumn or late spring), weather surprises happen, but on average, the temperature at night is not lower than +5 — +7 ° C.
  • For short-term trips to nature, both men and women can consider different temperature indicators when choosing a sleeping bag. Women can focus on t° comfort, while men can consider t° limit. It is important to assess the anticipated weather conditions and select a sleeping bag accordingly.
  • For extended hiking trips, it is advisable to have a temperature reserve (at least 5 degrees Celsius) in case of unexpected weather changes. Men can opt for a sleeping bag model based on t° limit to ensure extra protection.
Temperature specs are especially important during difficult hikes, during the changeable off-season and during mountain climbing.
  • For difficult expeditions such as mountain climbing, it is essential to have a temperature margin, which is not just recommended but mandatory. This is because mountainous regions often experience severe nights even during the summer season. Additionally, the physical exertion and fatigue associated with such expeditions increase the risk of freezing, even in relatively higher air temperatures. As a guideline, subtracting 10 °C from the weather forecast can be used to determine t° comfort or t° limit for women and men respectively.

While the EN 13537 and EN 23537 standards may have their limitations and not consider all factors influencing thermal insulation, they have greatly simplified the process of comparing sleeping bags based on temperature conditions. This allows buyers to conveniently select a suitable sleeping bag from various brands. However, it is important to consider other important criteria as well, such as the reputation of the manufacturer, which plays a significant role in establishing trust in the accuracy of the temperature ratings.