Anyone who has shopped for a sleeping bag is all-too-familiar with temperature ratings of sleeping bags. Unfortunately, as many people have also discovered, sleeping bag temperature ratings are often wrong—and sometimes very wrong.
While it’s always tempting to blame manufacturers for inaccurate labeling, there are many reasons a sleeping bag fails to keep everyone warm at a specific temperature. This article first explains how manufacturers obtain a sleeping bags temperature rating. Then the article explores other factors that affect a bags temperature rating. Additionally, you might wish to read other articles about sleeping bags on this site:
What Sleeping Bag Temperature Ratings Mean
A sleeping bag temperature rating is the manufacturer’s "best guess" how warm the bag is for the "average person." They arrive at a rating by giving bags to testers or employees, who then test the bags in various environmental conditions or in an "ice box."
|A Marmot goose down winter sleeping bag. For winter camping, goose down is the insulation of choice. See similar winter sleeping bags at Amazon.Com.|
However, the "average person" is a rare person. You see, the reason a temperature rating is never fully accurate is because people sleep at different body temperatures. If you are a "cold sleeper," then you are going to need a significantly warmer bag then someone who is a "hot sleeper.”
So what are hot and cold sleepers? The best way to understand the concept is to use sleeping at home in your bed as an example, in a house heated to 65 degrees.
Hot Sleeper – A hot sleeps with few if any sheets. They might use sheets at first, but as the night goes on, the sheets magically disappear. Also, hot sleepers gives off significant heat. If you have a bedtime partner and they complain about how warm you make the bed, then you are probably a hot sleeper.
Cold Sleeper – A cold sleeper goes to bed with every blanket piled on top of them, yet still wakes up cold. This happens because the person has a slow nighttime metabolism. Their body produces little body heat, so many blankets are need to stay warm.
Sleep Temperatures and the Sleeping Bag You Buy
Once you decide whether you are a "hot sleeper", a "cold sleeper" or somewhere in-between, the next step is to follow this “rough rule of thumb.”
Now, I’d like to stress that my rule of thumb isn’t scientific. Instead, it’s based on my own—and other’s—experiences. But, I do believe it is a good gage to follow.
Hot Sleepers - Assume the bags temperature rating is accurate for you.
Cold Sleepers - Assume the bags temperature rating is a minimum of ten degrees warmer than advertised. Thus, a bag that rated to 20 degrees will only keep a "cold sleeper" warm when the temperature is thirty degrees or warmer. And ten degrees may not be enough, depending on other factors.
For everyone else - If you fall somewhere between "hot" and "cold", then assume the bags temperature rating is at least 5 degrees warmer than advertised.
Other Factors That Affect a Sleeping Bag’s Temperature Rating
Getting the right bag to match your sleeping temperature is just the first step. You see, when the manufacturers give their bags temperature ratings, they make several reasonable assumptions. These assumptions include:
|A Marmot three-season synthetic sleeping bag. See similar bags at REI.|
A Sleeping Pad is Used - A sleeping pad is mandatory. Without a sleeping pad, a person is sleeping on the cold ground. No matter how "hot" you sleep or how warm your bag is, you'll still be cold without a sleeping pad. Moreover, manufacturers assume you sleep on a midweight sleeping pad that has an R Factor of 5 or greater. Midweight and “luxury weight” sleeping pads provide more insulation than lightweight sleeping pads (which typically have an R Factor of 4 or less). Read How to Choose a Sleeping Pad for more information.
Use of a Hood - If the sleeping bag has a hood (and most three-season bags do), the rating assumes the hood is used and drawn tightly over the users head. Remember, about 40-50% of a person’s body heat escapes from the top of their head. Also, using the hood is needed regardless of how much hair a person has “on top.”
Bag is Fully Zipped - This seems like common sense, but all ratings assume a full zipped sleeping bag. This contrasts to how many campers sleep—as many people leave their bags partially unzipped to provide a bit more room inside the bag.
Proper Sleeping Bag Size - When buying a bag, it is important to buy one designed for your height. If you are 5'10, do not get a bag that fits people up to 6'6. If a sleeping bag is too large, a pocket of cold air forms by the feet. This pocket of cold air keeps your feet (and thus you) cold all night long.
No Clothes! - Yes, temperature ratings really do assume you sleep in the "buff,” or at least wearing nothing but underwear. This is because sleeping while fully clothed often makes a person colder. In particular, cotton clothing is lethal to a sleeping bags temperature rating. Since cotton absorbs water, when a person sweats during the night their clothing absorbs the water. Once a person is wet, the sleeping bag has no hope of achieving its temperature rating. Worse, the person is likely to shiver all night and wake up wondering why.
If you want to sleep in your clothes (and I’ll confess, I do), sleep only in clothing made from moisture wicking material, such as fleece or polypropylene. I sleep in lightweight fleece pants, nylon underwear and a lightweight fleece shirt. On real cold nights, I may also use a fleece hat.
Regardless of what clothing you sleep in, just make sure you don’t sleep in cotton clothing.
Read the Fleece Clothing Guide to understand why cotton is just awful for camping and hiking.
In summary, it’s always better to buy a bag that provides an added 15-20° degrees of temperature rating. Doing so allows for use of the bag in a wider variety of temperatures. Also, a warmer bag allows the person to keep the bag partially unzipped and to sleep fully clothed if desired. Additionally, a warmer rated bag is crucial when using a lightweight, thin sleeping pad.
Remember, you can "open up" a bag that is a bit too warm to stay comfortable. But there are no effective methods to make a cold bag warm. Thus, to be safe, buy a bag that is a “bit too warm” than a “bit too cold.”
For general three season use, I suggest sleeping bags rated to a minimum of 15-20° degrees.
Online, there's almost too many places that sell sleeping bags - making it difficult on figuring out where to start shopping for one.
So let me make a suggestion. Begin shopping for a sleeping bag at REI. The REI website makes it easy to find/compare various synthetic/down sleeping bags at specific temperature ratings. Moreover, they provide detailed technical information about each bag - something that is sometimes missing at other online stores.
Other good online stores to buy sleeping bags from include:
- Amazon.Com - Amazon has an extensive selection of sleeping bags. Indeed, it almost has too many - making it difficult to browse. To browse sleeping bags on Amazon, I suggest checking out the "Good Brands of Sleeping Bags" section in the main Buyer's Guide to make shopping for a sleeping bag on Amazon easier.
- Cabela's.Com - Cabela's has a more limited line of sleeping bags, but does carry a few technical brands. Also a fine place to buy a "sleepover" bag for the kids.
- Campsaver.Com - Has frequent sales and a large selection.
- Eastern Mountain Sports