Sleeping Pad R-Value Explained
We break down sleeping pad R-value including how it’s tested, what it means for overall comfort and warmth, and tips for choosing the right pad
The sleeping pad you bring on an expedition can be the difference between a comfortable outing in nature and a sleepless night spent tossing and turning. But how do you decide which pad to buy and how much warmth you’ll need? Looking at R-value is a great place to start. R-value is the best indication we have of a pad’s ability to insulate, but can unfortunately be quite cryptic and confusing. Below, we answer many common questions about R-value, including how to choose, standardization and testing, cost, and more. For more, see our articles on the best backpacking sleeping pads and the best camping mattresses and pads.
What is R-Value?
If you were to lie directly on the ground while camping, you would quickly get cold due to the heat transfer from your warm body to the cold ground. Even a sleeping bag would not be an effective barrier, as your body would be compressing its synthetic or down insulation. Thus, sleeping pads serve as the protective layer between you and the ground—and they do so to varying degrees, depending on the pad’s thickness, insulation, and more. The pad’s level of insulation is denoted by its R-value.
Sleeping pads help to insulate you from the ground
Technically speaking, an R-value measures how well an object resists (hence the “R”) heat (this measurement isn’t only used on sleeping pads—it quantifies thermal resistance in windows, housing insulation, and much more). The higher the R-value of a sleeping pad, the greater it will resist heat transfer and keep you insulated from the ground. R-values for sleeping pads usually range from around 1 to 7, while thicker and less portable mattresses can creep into the double digits (but these have limited appeal for most backpackers). Keep in mind that this is a standalone rating system (i.e., R-value numbers have no correspondence to temperature).
Which R-Value is Right For Me?
R-values can be tricky to interpret, as they have no natural relation to temperature. Additionally, there are many other factors at play when it comes to your comfort, including the warmth of your sleeping bag, your metabolism (do you run hot or cold?), your sleeping position, the weather (is it wet or windy?), and more. Because it can be difficult to state with confidence what R-value is right for what temperature, we'll speak in generalities—and it never hurts to be conservative. Below, we list the three major seasons, giving the lower limits of each range for those looking for the lightest and most packable option. If you're not limited in space, weight, or price, consider opting for a higher R-value (unlike a too-warm sleeping bag, you're unlikely to overheat). The chart underneath provides examples of backpacking pads in each range.
Summer: 1 – 3
3-Season: 3 – 5
As we mentioned above, a few other factors will help dictate what R-value you need, including your sleeping position and surface. Sleeping on your back more evenly distributes your weight, while side sleepers might not get the most out of their pad’s R-value (if this sounds like you, a substantial, thick pad like the Sea to Summit Ether Light XT Insulated is a good option). In terms of sleeping on snow—a question we often receive—you don’t necessarily need a warmer pad. Snow is a very poor conductor, and bedding down on the white stuff can actually be a lot warmer than sleeping on dirt or rock in the winter. That said, it’s a good idea for all cold-weather camping to pair your air or self-inflating pad with a foam mattress for insurance in case of a leak. And the good news is that R-values are additive, so you get increased warmth when you stack multiple pads.
For winter camping, you'll want a pad with an R-value of 5 or more
Are R-Values Standardized?
This is an excellent—and timely—question. Up until last year, there was no standardization for how companies measured R-value. Therm-a-Rest and Sea to Summit, for example, had their own testing facilities, while brands like Exped used third-party researchers to do the testing for them. And some companies merely estimated their R-values. As a result, one brand’s 3.2 might have been another brand’s 4.5—meaning there was no way to compare pads with any accuracy. Further, some manufacturers (notable companies include Big Agnes and Nemo) forewent the R-value rating entirely, opting for temperature ratings instead.
Nemo and Big Agnes formerly used temperature ratings rather than R-values
The good news: that all changed in 2020. Thanks to Therm-a-Rest, REI, and MEC (Canada’s gear cooperative), there is now a standard for R-values, set in place by ASTM International (a global testing body). Similar to the ISO/EN rating for sleeping bags, the goal is to allow consumers to compare a variety of pads like for like. As of last year, REI and MEC now require that every pad they carry (which accounts for a large portion of the market) has an ASTM R-value, making ratings much more accurate and dependable across the board.
How is R-Value Tested?
Thanks to the new ASTM standard, we can now be assured that each pad we compare while shopping undergoes the same rigorous and standardized testing. In this testing, pads are sandwiched between a hot plate (35 degrees Celsius) on top, which mimics the body, and a cold plate (5 degrees Celsius) underneath, mimicking the ground. Over the course of four hours, testers measure how much energy the top plate uses in order to stay at a consistent 35 degrees. The less energy it takes, the more insulative the pad. The more energy it takes, the less insulative the pad.
Most high-quality pads have undergone testing for warmth
Does a Higher R-Value Cost More?
Having a sleeping pad with a higher R-value than you need certainly won’t hurt, but it will almost always come with a weight penalty and price increase. This will likely be an issue for ounce-counting ultralighters and even for the everyday backpacker on longer trips where weight can add up quickly. For example, the Exped DownMat XP 9 with an R-value of 7.8 comes in at 1 pound 15.6 ounces and costs a pricey $229, while the Therm-a-Rest NeoAir XLite (R-value: 4.2)—which will suffice for most 3-season trips—shaves off 1 pound 3.6 ounces and $39. And keep in mind that you can always use a layered set-up—a 3-season air pad and a lightweight closed-cell foam pad, for example—which lends versatility in addition to warmth. But in the end, if you don’t mind the added weight or cost, a sleeping pad with a higher R-value is certainly a nice piece of gear to own.
Layering with a foam pad can provide an extra dose of warmth
The Impact of your Sleeping Bag on Warmth
When choosing a sleeping pad, you should factor in the sleeping bag you’ll be using, too. The two work as a sleep system, and if you buy a bag without focusing on the temperature rating or a pad without considering the R-value, you won’t be maximizing their potential. When we go backpacking, we think of our sleeping bag and pad as one unit by taking into account both the sleeping bag rating and pad R-value. In fact, Therm-a-Rest designers claim that you actually need a pad with an R-value of at least 4.0 to maximize your sleeping bag’s temperature rating. In other words, if your sleeping bag is rated to 20 degrees Fahrenheit, you need a pad with an R-value of 4 or higher in order to be comfortable at 20 degrees. And of course, it’s always important to factor in the type of backpacking tent and the layers you’ll be wearing to bed, too.