What is a Sleeping Bag Temperature Rating?
By Mark Rocco
Temperature ratings are used to classify sleeping bags based on the coldest temperature at which they will keep the average person warm. Although there are many different factors that go into making this rating, such as the style of the bag (rectangular of mummy), the type and quantity of fill, and heat conserving features (hood, baffles, zipper tube, etc), the advertised temperature rating is still nothing more than a best guess.
So how exactly do manufacturer's guess what the temperature rating should be. Quite simply, they get volunteers to sleep in them under a variety of different temperatures, and calculate (based on the subjective volunteer feedback) the lowest temperature that the 'average' person would be comfortable at.
So how does this help you when you go shopping for a sleeping bag? You first need to determine if you are an average sleeper. This really has nothing to do with getting the recommended 8 hours of sleep every night, but more to do with the number of sheets you require to keep you warm. The best way to illustrate this is to look at the extremes, so that if you fall in the middle, you are average.
A 'hot' sleeper, is someone who typically will sleep covered in nothing more than a sheet, no matter what the temperature. This is due to the fact that their night time metabolism remains high and their body continuously generates so much heat they almost always hot. Men tend to be hot sleepers.
The opposite, naturally, is the 'cold' sleeper. These people are easily recognised by the pile of sheets and quilts needed to remain warm during the night. For this group (typically women), their night time metabolism drops significantly generating very little bodily warmth, which needs to be conserved under piles of blankets to remain comfortably warm at night.
So with this in mind, what is an average sleeper? Quite obviously, someone who needs more than a sheet, but less than a stack of blankets to sleep warm on cold nights. Since temperature ratings range from approximately +40F to -20F, you'll need to select a sleeping bag based on how you sleep (hot, cold or average) using the manufacturer's temperature rating as a starting point. Hot sleepers can select a sleeping bag based on the rating as is, while cold sleepers should add an extra 10 - 20 degrees. For example, if you're a cold sleeper looking for a sleeping bag that will keep you comfortably warm in temperatures as low as 30F, you will want to select one that is temperature rated down to at least 20F (possibly as low as 10F if you really pile on the blankets at night).
No matter what climate you plan to be sleeping in, remember that a sleeping bag's temperature rating is simply a best guess for the average person. Remember to purchase accordingly and your nights under the stars will be warm and comfortable.
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