When you got and take a look at the different sleeping bags for sale on your local outdoor gear retailer or online, you will notice that they have labels (either sewn into or printed on the bag) showing their sleeping bag temperature rating. Many first-time buyers often ignore these sleeping bag ratings simply because they don’t understand what they mean. However, these temperature ratings are one of the most important things you need to consider whenever you go shopping for a new sleeping bag. So to help you make sense of these numbers, we’ll try to translate these laboratory-generated numbers into relevant and digestible information. This way, you can grasp their significance and understand what they mean for your nights at the camping grounds. Armed with such information, you should be able to better decide whether or not a particular sleeping bag is both safe and suitable for your intended destination.
Manufacturer’s Minimum Temperature Ratings
Before there were any standardized methods of rating sleeping bag temperatures, the manufacturers themselves assigned temperature ratings to their products (whether that’s a backpacking sleeping bag or a full-blown camping sleeping bag) based on their own testing methods and standards. More often than not, these methods included everything from sleeping in a temperature-controlled meat locker to real-world testing experience. And even after the widespread adoption of the EN testing standard for sleeping bags, many sleeping bag manufacturers still provide their own temperature ratings alongside the European Norm (EN) ratings.
How the Manufacturer’s Minimum Temperature Ratings Is Tested
The manufacturer’s minimum temperature rating is assessed by the brand itself and not by a third-party evaluator. Different manufacturers will label or refer to their temperature ratings differently. Some manufacturers refer to them as ‘Sleep Limit’ or ‘Sleep Zone’, while others simply call it ‘Bag Temperature’. These in-house ratings may or may not be (depending on the manufacturer) based upon several criteria including other temperature-rating tests and the real-life experiences of their personnel who are tasked to test the bags outdoors. That said, the result of the test may vary by a few degrees from one brand to another considering that the tests were implemented by various people who differ from one another in terms of body type, age, and gender.
Because of the variation in different brands’ testing methods and testers, it often happens that the ratings produced range anywhere from conservative to inflated. That said, these in-house ratings are at best a rough guide for picking the right sleeping bag. For the same reason, campers usually have a hard time (nearly impossible for others) reliably compare sleeping bags across brands.
Using the Manufacturer’s Minimum Temperature Ratings
Despite the seeming inaccuracy of the manufacturer’s minimum temperature ratings, it should still be treated as a safe alternative to EN’s ‘Extreme’ rating in establishing the lower end of a sleeping bag’s safe temperature range.
That said, when you’re shopping for a new sleeping bag, be sure that its manufacturer’s minimum temperature rating is comfortably lower than the lowest temperature you’re likely to encounter at your camping destination. For example, if you’re going somewhere where the temperature could drop to 0°C, be sure to buy a sleeping bag with a manufacturer’s minimum temperature rating of 0°C (preferably lower).
European Norm (EN) Temperature Ratings
All sleeping bags being sold in Europe were required to be checked for warmth or thermal ability as per regulation under the European Norm (EN) 13537. This is the standard temperature rating system for sleeping bags devised in the early 2000s and updated around 2012. The EN rating was intended to standardize and simplify the system for sleeping bag temperature ratings, which was hoped to provide a coherent rating system that cuts across the differences among the different brands’ minimum temperature ratings.
The EN standard measures the following four temperature ratings:
- Upper Limit. This is the highest temperature at which a standard adult male can enjoy a comfortable night’s sleep without feeling too hot and sweating excessively inside the sleeping bag. This is measured with the zips and the hood open and with arms outside of the sleeping bag.
- Comfort Rating. This is the temperature at which an average adult female can expect to sleep comfortably in a relaxed position. The rating is based on what is considered a ‘standard woman’ as they have a lower tolerance to the cold than a ‘standard man’.
- Comfort Limit. This is the temperature at which a standard male can sleep for eight hours in a curled position without waking. This rating is the lower threshold for a continuous and undisturbed night’s sleep.
- This is the minimum temperature at which a standard woman can remain for six hours without risk of death from hypothermia. At this temperature, sleep will be severely disturbed. Also, this temperature is where frostbite is most likely to set in.
How the EN Temperature Ratings Are Tested
The tests revolve around the idea that subjects (i.e. campers or any other person using the sleeping bag) will be able to get the best out of the sleeping bag by adjusting their sleeping position and minimizing thermal loss. With the assumption that users know the limiting aspect of their sleeping bags, they will be able to protect themselves from such factors and any hazard that comes along with them.
To come up with the temperature ratings, tests are carried out in a laboratory using a standard thermal dummy. The dummy is dressed in usual camping clothing (e.g. a warm base layer top and trousers) and in knee-high socks, all of which have specific thermal insulation.
Unlike the manufacturer’s minimum temperature ratings where the tests are conducted by the manufacturer’s in-house team, EN testing is conducted by a third-party evaluator. And because the tests are done in internationally certified labs using standardized testing methods, the resulting ratings can be relied upon to provide a fairly accurate guide to what temperature range a sleeping bag is best suited to perform in. Also, standardized testing allows you to reliably compare sleeping bags from different manufacturers. This way, regardless of the brand or manufacturer, you will be able to better pick the right bag to suit your needs.
Using the EN Temperature Ratings
Although all the ratings mentioned earlier have their own significance, many campers usually focus on two main numbers: the EN comfort rating and the EN lower limit rating. As stated above, the bag’s comfort rating indicates the lowest temperature in which the average woman can sleep comfortably in that bag while the lower limit rating indicates the lowest temperature in which the average man will sleep comfortably in that bag. The reason why most people focus only on these two numbers is that all they really want to know is the lowest temperature that they can use the sleeping bag. The other ratings are still important, though they’re treated more like secondary information.
ISO 23537-1:2016 Ratings
The ISO 23537-1:2016 is an international standard that is used in testing the warmth of sleeping bags. It was introduced as an updated version of the EN ratings and serves as the new testing protocol for all sleeping bags going forward. The ISO rating measures the following variables:
- Comfort Temperature. This refers to the lower limit of comfort range where a sleeping bag user with a relaxed posture (such as lying on their back) will feel comfortably warm. This should be the coldest temperature that a ‘cold sleeper’ would want to use their sleeping bag for.
- Limit Temperature. This refers to the lower limit where the user with a curled body sleeping position would feel comfortable. That said, this would be the coldest temperature that a ‘warm sleeper’ would want to use their sleeping bag for.
- Extreme Temperature. This is the low temperature where the sleeping bag user will possibly be at risk of hypothermia. If you think that the temperature will drop lower than the rating specified in your sleeping bag, you should consider getting a new and more appropriate one.
- Transition Range. This is the temperature between comfort temperature and the limit temperature.
- Risk Range. This is the range of temperature between the limit temperature and the extreme temperature.
How ISO Ratings Are Tested
Testing is done like EN testing procedures. That is, the test is conducted in laboratory conditions with a thermal dummy dressed in a thin thermal top, long johns, and socks. The thermal dummy is then inserted into the sleeping bag atop a basic foam mat, and as temperatures in the cold chamber drop, corresponding measurements are recorded and evaluated. Basically, the tests look at factors like when the manikin’s heat accumulates in the sleeping bag and the range where its temperature remains relatively steady. Testers also measure the point at which heat begins to be lost, and then when it is lost at a rate where the bag is deemed no longer effective.
Making Sense of the Numbers
The temperature ratings above should provide you with a good idea of just how effective a particular sleeping bag will be in any given circumstance. But then, even with the descriptive titles, it can still be rather confusing for the new camper. That said, you may want to focus on the actual numbers presented instead of figuring out what ‘upper limits’ or ‘risk range’ mean (although it is strongly advised that you be familiar with them.
-40° F TO +4° F Sleeping Bags
Sleeping bags in this range are your best bet for camping in cold places or during the colder months of the year. If your camping destination features snow and ice, you’ll want to bring a sleeping bag under this category. Winter sleeping bags like these will typically feature ‘warmer’ features like high-grade down or synthetic insulation, high fill value, and draft eliminating features like zipper baffles and collars.
+5° F TO +29° F Sleeping Bags
‘Three-season sleeping bags’ fall under this category, and as the name suggests can be used almost throughout the year. Whether you’re multi-day hiking in the early spring, backpacking in the summer, or going for the last camping trip before the snow starts falling, a sleeping bag in this category would be a good choice.
+30° F TO +55° F Sleeping Bags
Sleeping bags in this category are used when camping during summer and in warmer destinations, especially those in low to moderate elevations. Because they don’t need and contain a lot of insulation to keep the user warm, they will generally weigh much less than the other sleeping bags mentioned above.
Are These Numbers Really Reliable?
Considering that these ratings are pretty much accepted by most (if not all) manufacturers around the world, the numbers should be reliable enough to be trusted. However, remember that these ranges are just ‘standards’, the meaning of which will vary depending on a person’s own perception and understanding of the word.
Also, it should be noted that there are a lot of factors that will come into play when it comes to measuring just how warm you’ll be inside the sleeping bag. For instance, the amount and type of clothing you wear to sleep will certainly affect how warm you will be throughout the night. Also, consider the insulation underneath your sleeping bag. Using a cheap and low-quality sleeping pad will definitely cause you to feel cold since it is generally accepted that the insulation underneath you is worth twice that of insulation over you. Of course, there’s also the environment (i.e. campsite and weather conditions) to consider.
All these variables and many others like it will have dramatic effects on how warm you’ll be inside the sleeping bag and how the temperature ratings will be perceived and felt.
Globo Surf Overview
Years ago it was pretty common for campers to experience and endure cold nights at the campsite mainly because of the inaccuracy and variety of sleeping bag temperature ratings. Today though sleeping bag manufacturers are required to give clearer and more accurate sleeping bag ratings for their products, which is immensely helpful in providing campers an idea of what comfort and limit temperatures their bag can be used in. Just remember that these ratings are to be taken more as a guide than a rule set in stone. There are several other factors to consider that will affect the temperature rating assigned to any particular sleeping bag. Despite these variables, having a good understanding of what these ratings stand for will allow you to choose a sleeping bag that will best suit your type of camping adventure.
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