Sleeping bag ratings can be a bit confusing. So, If you don’t mind, I’d like to share with you what I have learned about them.
When we talk about sleeping bag ratings we are talking about an industry standard that does not apply equally to everyone.
A sleeping bag with an advertised rating of 30°F doesn’t mean that you will sleep comfortably at 30°F. Much of your comfort depends upon at least three things.
- How well hydrated you are.Hydration is critical to a body functioning properly. And in the winter we tend to neglect our hydration, drinking only when we get thirsty, primarily because we connect the need for hydration with heat and sweating. It’s just as important in the cold to stay properly hydrated because water is a critical component of our body’s functions, and when we have enough of it in our system, it can work properly in burning the fuel (food) we give it to keep ourselves warm.
A simple test on how well hydrated you are is to look at the color of your urine. Orange means that you need more water; the darker the shade of orange the poorer your hydration level. Clear means that you are well hydrated. Proper hydration does not happen immediately. Here is a link to an article about getting properly hydrated, “How to Hydrate When Dehydrated“
- How fast you metabolize, or how hot you burn.Some people naturally sleep hotter than others, and generally men sleep hotter than women.
“According to an article published in the Journal of Applied Physiology, men have a metabolic rate that’s about 23 percent higher than women’s. Your metabolism is the rate at which you burn food to fuel the body, and as a by-product of that process, you heat up the body. So women’s bodies are colder than men’s because [women’s] metabolisms are slower…” – (from this article)
A great example of this principle in real life is me and my wife. Even though the temperature in our bedroom is the same for both of us, at night she is putting ON blankets, while I am often taking them OFF. Some of you may have had this same experience.
So, a sleeping bag rated at 30°F for a man is going to feel very different for a woman. And not only that, but metabolism rates between individuals of the same gender differ. It’s important to know what rating your bag will need to be based on your experience and relative to the advertised rating of the bag. So, when the bag is advertised as rated to 30°F, your experience may tell you, “Get the bag rated at 10°F”.
- What clothing you are wearing when you get into your bag for the night.If you are wearing cotton, you can be certain that you will sleep colder than someone who is wearing polyester, wool, or down. The reason for this is because we are constantly perspiring. That perspiration as it leaves your body doesn’t magically disappear; it has to go somewhere, and cotton LOVES to hang on to moisture (your perspiration). With that cotton fabric against your skin collecting that perspiration, it is going to get damp. And that dampness is going to (for lack of a better word) suck the heat from your body. The other factor in this point is how much insulation you are wearing on your body when you get in to your bag for the night. More insulated clothing means that your sleeping bag can have a higher rating. It comes down to how much total insulation and the quality of that insulation you have around your body when you go to bed.
Ultimately a sleeping bag’s rating gives you a starting point, assuming that the manufacturer is using an industry wide rating standard. This rating coupled with your experience will help you chose a sleeping bag rating that will be more accurate for your needs.
I hope you found this helpful.
If you have any questions about this, or other cold weather or sleeping bag topics, feel free to ask. I am always open to topics that interest you.