Sometimes we use activity trackers for measuring how you sleep, but this is often just a way to measure the symptoms but not the cause of sleep. When is comes to sleeping, temperature can make a huge difference on how well you rest. This should come as no surprise for anyone who has ever woken up in a sweat on a hot summer night, or been shivering when they awoke in a cold tent.
With camping or sleeping outdoors checking the weather for temperature and precipitation is one of the most important plans. Sadly it is sometimes hard to tell what to do with the information, especially when it comes to figuring out of the weather will make you cold or warm given your sleeping bag and gear. Since having a bad nights sleep can wreak havoc on your overall wellness and quickly turn a fun trip into a nightmarish slog, it is important to plan appropriately.
But how do you know what to prepare for? Once you check the weather and identify how hot or cold it is going to be, and if there is precipitation, what do you do with that information. For many it means checking that their gear is appropriately rated for the weather. To do that you have to better understand what a rating for a sleep bag is!
What is a sleeping bag rating system?
For the most parts manufacturers can use whatever system they want to make and label a sleeping bag. This is extremely frustrating when trying to compare two sleeping bags since one might have a “comfort rating” and another a “risk rating” temperature labeled. Are comfort and risk the same thing? While yes and no, both may correspond to a test on the same testing standard but they will not fit the same definition. Even with that, not all sleeping bags adhere to a testing standard.
If you are purchasing or comparing sleeping bags the best thing to do is ensure that they adhere to similar standards and use the same testing to come up with their ratings. The two major standards are ISO and EN rating, while the standards are mostly the same their definitions and testing methods vary slightly and have even shifted over time. .
EN 13537 – This is the European norm standards that relates to sleeping bag labeling. (Wikipedia EN 13537)
ISO 23537 – The International Standards Organization requirements for sleeping bag labels. (ISO 23537, Updated 2022)
Most sleeping bags are designed with a rating, that identifies a temperature they work at or are comfortable at. But those that contain the ISO or EN marks and numbers are showcasing that they have adhered to the lab testing standards of the guidelines and makes it easier to compare.
Even for sleeping bags using the testing standards it is important to note that these are designed to define the general heat transfer of a bag. Heat transfer is a complicated topic though, and lab settings are unlikely to match the exact parameters of where you are using the bag. Things like high altitude (which changes the air pressure), the humidity of the area, and the ground preparation of your tent and sleeping mat can all make huge impacts on how the sleeping bag rating compares to how you feel thanks to the change in heat transfer.
The ratings break down into ranges, but again there is no requirement on which range to use in marketing. While some manufacturers use the comfort range, you can at times see the transition range or risk range used in the name of the bag. The naunces of how different weather are not capture in the ratings, but the idea of differing heat transfer based on different body positions at least is. It is worth understanding how these ranges are defined by the standards to figure out what they really mean:
Comfort Rating: The lower limit down to which a sleeping bag user with a relaxed posture, such as lying on their back is…at the threshold of feeling cold.
Lower Limit: The lower limit at which a sleeper in a curled-up body posture is at the threshold of feeling cold.
Risk Range or Extreme: The lower limit at which the risk of hypothermia is possible, measured on a 6 hour basis.
It is clear from these standards that the ranges change drastically on how to interpret the numbers. Thankfully the naming is pretty clear and for the most part getting a sleeping bag that has a comfort rating temperature that is below what you expect to encounter covers the most likely scenarios.
What Rated Sleeping Bag Do I Need?
When considering which sleeping bag to buy based on rating, the other pieces to take into consideration are Price, Weight, ability to modify. As mentioned above, you should get a sleeping bag with a comfort rating using an ISO or EN standard that is a few degrees below the lower limit temperatures you expect to encounter. Doing this give you the most versatility to use the bag in warmer weather by just keeping it open or using it as a blanket. If you can’t afford the lower limit or if you are only encountering colder temperatures for a night or a fraction of a night then sleeping in a curled tight position or supplementing with additional liners or blankets may extend the comfort level well.