When choosing a sleeping bag there are a few things you take into account. The cost, style, color, and things like that are important of course. But what you really want to know is how comfortable and how warm it’s going to be.
Am I right?
I know that’s my main two criteria. (as well as color, I’m big on color-coding my gear).
It can get a little bit confusing without actually trying a sleeping bag, however. With the various season ratings, estimated temperatures, GSM ratings, and so on.
In this article, I’m answering a specific question someone asked me recently that provides a good baseline for sleeping bag temperatures:
What is a 250GSM sleeping bag temperature? This is hard to answer because the GSM (Grams per Square Meter) of a sleeping bag doesn’t directly relate to the temperature. You need to also take into account the shape, size, outer layers, materials, etc. I’d estimate a good quality 250GSM bag is good for 2-seasons (5C and above).
Understanding Sleeping Bag Categories by Temperature
As I explained above, while a sleeping bag might give you the GSM rating there it’s a lot more to take into account to get a good idea of how warm you’re going to be.
Sleeping bags are typically categorized by what seasons are recommended for as follows:
|One season||Summer||10 °C and Up
|Two seasons||Late Spring/Early Autumn||5 °C and Up
|Three Seasons||Spring through Autumn||0 °C and Up
|Four Seasons||Winter||5 °C and Up
As you can see from above table, sleeping bags are designed for certain seasons because they are capable of handling certain weather conditions. It’s a general rule, however, so you need a good idea of the temperatures you’re going to be camping in.
The more Seasons the bag is recommended for the wider fluctuation in temperature the bag provides. There are also some other classifications that fall within the season rating, and this is where you’ll probably hear about the GSM.
Related: I covered some useful tips on how to increase your sleeping bag warmth here.
What GSM Should I Look for in a Sleeping Bag
The GSM you look for comes down to the preference of feel more so than temperature. I explained above how you look for different temperature ratings through the various Seasons which is a standard for sleeping bags.
The higher the GSM the thicker a denser the filling will be. So, technically you can have various GSM rated sleeping bags that are all capable of providing the same temperatures, but the feel and weight of the bag might be very different.
I hope this is making sense. So, in my opinion, when looking for a sleeping bag you should look for the season and associated temperature range first that will be appropriate for the temperatures you will be camping in. Then look at the GSM to get an idea of how dense the filling is.
There is some correlation overall, of course. More often than not the higher the GSM, the warmer the sleeping bag will be. But as a cautionary note, due to a few other factors as I’ve highlighted in this article, it may not always be the case.
Looking for a more heavy-duty sleeping bag? Check out this post where I explain what 400GSM means for a sleeping bag!