You’ve probably encountered it in your search for the right sleeping pad for your long-distance hike: the R-value. But what does it actually mean? And what R-value is right for you and your long-distance hike? Let’s clarify that and more in this article.
Table of Contents
The R-value
The Importance of Sleeping Pad R-values
A sleeping pad has several important functions. Not only does it enhance your sleeping comfort during backpacking, but it also helps to keep you warm and prevents hypothermia by stopping the ground from absorbing your body heat. While the comfort of an insulation mat is subjective, it is possible to objectively compare how warm different sleeping pads keep you. This is where the R-value comes into play.
The R-value (R for resistance) is a measure of the thermal resistance of an object (i.e., the sleeping pad). Basically, the R-value tells you how much resistance the sleeping pad provides against your body heat escaping to the cold ground. In other words, the R-value is a measure of the insulating performance of a sleeping pad.
The higher the R-value, the higher the insulation performance and the smaller the heat loss to the ground. Most commercially available insulation mats have an R-value ranging between 0.5 and 8.
The ASTM F3340-18 Standard
For a long time, there wasn’t a unified way to measure the R-value. The approach to measuring the insulation of a sleeping pad varied from manufacturer to manufacturer. Due to these different measurement methods, a cross-manufacturer comparison of sleeping pads was only of limited use.
To address this issue, a group of industry leaders came together in 2016 to establish a standard method for measuring the R-value of sleeping pads. The result was the ASTM F3340-18 standard (latest version, ASTM F3340-22).
When measuring the R-value using ASTM F3340-18, the test mat is sandwiched under constant pressure between a heating plate (simulating body heat at 35°C) and a cold plate (simulating the ground at 5°C). With the help of electronic sensors, it is measured over 4 hours how much energy is needed to keep the temperature of the heating plate constant. The R-value is then calculated from the energy input. The smaller the energy input, the higher the R-value. Due to the standardized procedure, the measured values can be reproduced and thus allow a comparison between sleeping pads of different manufacturers.
The ASTM F3340 standard was published in late 2018 and has been in use by most major manufacturers since early 2020. However, it is not compulsory to use this standardized procedure. So when buying a sleeping pad for your long-distance hike, you want to make sure that the R-value has been measured according to ASTM F3340-18.
What’s the Right R-value for Your Long-Distance Hike?
It is difficult to give a general R-value recommendation for an area of use. Manufacturer recommendations sometimes differ greatly from each other. This may be due to the different measuring methods in the past, but there are additional reasons that we’ll delve into later on.
Especially for trekking novices, however, an overview can still be helpful. So here’s a rough overview of the R-values, their areas of use, and rough temperature recommendations.
The values in the table are set rather low. If you’re not sure, better pack a sleeping pad with a higher R-value for your next long-distance hike. Since body heat is also lost laterally when you sleep, it’s very unlikely that you’ll get too warm right away with a slightly higher R-value.
| R-value | Range of Application | Minimum Air Temperature |
|---|---|---|
| 0,5 | Trekking tours in high summer and in very hot climates | +15 °C / 59 °F |
| 1 | Trekking tours during the summer, depending on climate and weather also for warm spring and autumn nights. | +7 °C / 45 °F |
| 2 | Trekking tours during spring to autumn in mild weather without ground frost | +2 °C / 36 °F |
| 3 | Trekking tours from spring to autumn, possibly also during mild winters | -5 °C / 23 °F |
| 4 | Suitable for all 4 seasons, can be used for long-distance hiking in winter | -11 °C / 12 °F |
| 5 | Trekking tours during cold winters | -17 °C / 2 °F |
| 6 | Trekking tours in very cold winters and cold climates, e.g. high alpine long-distance hikes | -24 °C / -11 °F |
| 7 | For expeditions to areas with extreme cold (e.g. the Arctic) | -32 °C / -26 °F |
| 8 | For expeditions to areas with extreme cold (e.g. the Arctic) | -38 °C / -36 °F |
| 9 | For expeditions to areas with extreme cold (e.g. the Arctic) | -45 °C / -49 °F |
| 10 | For expeditions to areas with extreme cold (e.g. the Arctic) | -50 °C / -58 °F |
Factors Influencing the Required R-value of the Sleeping Pad
Ground Temperature and Weather on the Trail
At least as important as the air temperature for the required R-value is the ground temperature, because your sleeping pad is supposed to protect you from heat loss to the ground. If possible, check how cold the ground temperatures are in your trekking area before you start your long-distance trek.
Another influencing factor is humidity and wind speed, because these influence how warm you feel. When the humidity is high and the wind is strong, the same temperature will feel cooler because your body heat is being dissipated faster.
Type of Accommodation/Sleeping Place During Trekking
The R-value you need for your long-distance hike also depends on the type of sleeping place. Do you want to sleep directly on the ground or is there another layer between the sleeping pad and the ground ( for example the tent)? Are there leaves on the ground that provide additional insulation or are you lying on stone or frozen ground?
Sleep Type/Sleeping Habits and Gender
Your sleep type affects what R-value you will need. Women, in particular, tend to have a harder time retaining body heat and need higher surrounding temperatures for sleeping. Therefore, it is recommended for “warm sleepers” to choose a slightly higher R-value (about 0.5 to 1.0 higher). Additionally, sleeping position (how much body contact do you have with the sleeping pad?) can impact the required R-value, with side sleepers losing more heat than back sleepers. Since side and stomach sleepers also put more pressure on one spot of the sleeping pad, a very thin sleeping pad may be uncomfortable.
Sleeping Bag
Another factor to consider is the choice of sleeping bag for your long-distance hike. When choosing a sleeping pad, you should consider the temperature rating of your sleeping bag. Some manufacturers even explicitly recommend an R-value of ~4 so that the sleeping bag can deliver its full thermal capabilities. It’s worth noting, however, that many (not exactly cheap) high-end sleeping pads are in this R-value range. Still, make sure your sleeping bag and sleeping pad are a good match to maximize their capabilities.
Limited: Comfort, Thickness and Weight
Although the R-value does not generally indicate the thickness and comfort of a sleeping pad, sleeping pads with a higher R-value (approx. from 3.5) are often thicker and more comfortable than insulating mats with lower values. Conversely, however, one cannot conclude the R-value from the thickness of an sleeping pad. It depends on many other factors, such as the type of padding, properties of the material or surface structure.
Since thicker sleeping pads are usually heavier, however, you have to trade off comfort for extra weight in your backpack—as is often the case when trekking.
Sleeping Pad Price
For long distance hikes on a budget, the price of a sleeping pad is an important factor. High R-value sleeping pads tend to be more expensive than those with a low R-value. For those who don’t need to rely on a sleeping pad with a high R-value due to low temperatures on the trail and are willing to sacrifice comfort, this is where you can save money.
Stacking R-values
The R-values of insulation mats are considered to be additive. This means one can layer a sleeping pad with an R-value of 2 and one with an R-value of 3 to achieve a total R-value of around 5. This can be useful if you want to protect an inflatable sleeping pad from damage on rocky terrain on the trail and place a flat pad underneath it.
Limits of the R-value
Just because a sleeping pad has a high R-value doesn’t necessarily mean it’s a good product. The R-value only provides information about the insulation performance. Whether the sleeping pad is comfortable, robust or durable cannot be deduced from the R-value. So when choosing your sleeping pad, don’t just look at the R-value.
Conclusion
We hope that our blog post about R-value in sleeping pads has been helpful in finding the right sleeping pad for your long distance trekking tours. We regularly test equipment on our blog. Take a look at our product test for the ultra-light Nordisk sleeping pad!
