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.
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.
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).
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 warmth, 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, it never hurts to go with 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
- Winter/4-Season: 5+
R-Values of Popular Backpacking Pads
|Backpacking Sleeping Pad||Price||Pad Type||R-Value||Season(s)|
|Exped AirMat HL||$129||Air pad||1.9||Summer|
|Therm-a-Rest NeoAir UberLite||$180||Air pad||2.0||Summer|
|Therm-a-Rest Z Lite SOL||$45||Foam||2.8||Summer|
|REI Co-op Stratus Insulated||$80||Air pad||2.9||Summer|
|Therm-a-Rest NeoAir XLite||$170||Air pad||3.2||3-season|
|REI Co-op Flash 3-Season||$100||Air pad||3.2||3-season|
|Sea to Summit Ether Light XT||$190||Air pad||3.2||3-season|
|Exped SynMat HL||$169||Air pad||3.3||3-season|
|Therm-a-Rest NeoAir Trekker||$130||Air pad||3.0||3-season|
|Sea to Summit Ultralight Insulated||$130||Air pad||3.3||3-season|
|Nemo Tensor Insulated||$160||Air pad||3.5||3-season|
|Sea to Summit Comfort Light Insulated||$180||Air pad||3.7||3-season|
|Therm-a-Rest Trail Pro||$100||Self-inflating||4.0||3-season|
|Sea to Summit Comfort Plus SI||$140||Self-inflating||4.1||3-season|
|Klymit Insulated Static V Lite||$95||Air pad||4.4||3-season|
|REI Co-op Flash Thermal||$129||Air pad||4.7||4-season|
|Nemo Tensor Alpine Air||$225||Air pad||4.8||4-season|
|REI Co-op AirRail Plus||$100||Self-inflating||5.0||4-season|
|Therm-a-Rest NeoAir XTherm||$200||Air pad||5.7||4-season|
|Exped DownMat XP 9||$229||Air pad||8.0||4-season|
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 Big Agnes Q-Core SLX 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.
This is an excellent—and timely—question. Up until recently, there has been no standardization for how companies measure 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. Some companies 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) have foregone the R-value rating entirely, opting for temperature ratings instead.
The good news is that this is all changing. 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). Like the ISO/EN rating for sleeping bags, the goal here is that consumers will be able to compare a variety of pads like for like, instead of making guesses about how one pad's R-value compares to another's R-value or temperature rating. And starting in 2020, REI and MEC will require that every pad they carry has an ASTM R-value. Therm-a-Rest has already adopted the new standard, with the ASTM rating visible on the 2020 updates of their pads.
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.
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 HL Winter with an R-value of 7 comes in at 16.9 ounces and costs a pricey $229, while the Therm-a-Rest NeoAir XLite (R-value: 3.2)—which will suffice for most 3-season trips—shaves off 4.9 ounces and $59. 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.
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.
See the Best Backpacking Sleeping Pads See the Best Camping Mattresses and Pads