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Understanding R-Values for your Sleeping Pad


Article Categories: Gear
Article Tags: Camping Tips | Hiking

If you have ever gone camping and woken up in the middle of the night shivering and freezing cold it might be because you have the wrong sleeping pad. Specifically, it might be because you have a sleeping pad with the wrong R-value. This single value is one of the most important attributes of any sleeping pad for camping yet it also remains poorly misunderstood by many new and experienced campers.

Thankfully, a brief review of R-Values and their implications is all it takes to be brought up to speed. An understanding of R-values, and the role they should play in selecting a sleeping pad, can help save you the worry and risk of body heat loss and even hypothermia. It is simply that important.


What Is An R-Value?

An R-Value is a significant measure of the thermal resistance of something and it applies to more than just sleeping pads. Everything from the insulation of your house to the glass on a car can have an R-Value. Engineers pay very close attention to this number and you should too.

R-Values basically tell you how well a substance can stop or slow the movement of heat from one side of that substance to the other. Heat can move in different ways such as radiation, think of the heat you feel from a warm fire, and convection, as happens with warm air rising and cold air sinking. R-values measure resistance to a third form of heat movement called conduction.

Conduction is direct heat transfer through a substance. This is what happens when the handle on a boiling pot of water gets too hot to grab. Heat transfers from the stove to the metal of the pot, and into the handle. This is also how your body rapidly loses heat when sleeping on the cold hard ground during a camping trip. Having a sleeping pad with the appropriate R-value for the environment you are in can prevent this.


How Are R-Values Determined?

There are two ways that R-values are determined. Many companies estimate the R-value of their pads based on several construction and design factors. However, thanks to a new industry standard, there is now a precise way to calculate the R-value. This standard has only been around for 3 years, so it is still relatively new, and many companies aren’t using it yet.

To estimate the R-value of a sleeping pad, several factors are taken into account:

  • Material and Thickness: The type of material used in the sleeping pad greatly influences its R-value. Foam, air, and self-inflating pads all have different insulation properties. Furthermore, the thickness of the pad’s material plays a significant role. Generally, thicker pads offer higher R-values as they provide greater resistance to heat flow.
  • Construction and Design: The design and structure of the pad affect how efficiently it retains heat. Baffles, chambers, and patterns of air or foam distribution all impact the R-value. Well-constructed pads minimize heat loss and maximize comfort.
  • Compression: Sleeping pads are often compressed under the weight of the sleeper. Manufacturers test the R-value under ideal, uncompressed conditions, but it’s crucial for users to understand how their bodies might compress the pad and affect its insulating properties.
  • Environmental Factors: R-value testing should consider real-world conditions, including the effect of moisture, humidity, and temperature fluctuations.

To get a good estimation of R-value, manufacturers test their sleeping bags in controlled environments. The R-value then becomes a reference point for consumers to choose the right sleeping bag for their specific outdoor adventure, taking into consideration the expected temperatures and weather conditions they will encounter.


Industry Standards

However, estimation is just that- a good guess. If you really want an accurate measure of your sleeping pad’s performance, you need to look for adherence to industry standards. Until 2020, there was no industry standard for the R-value of a sleeping pad. But in 2020, the outdoor industry adopted a standard called ASTM F3340-18. This standard is internationally recognized and has led to an industry-standard test for determining R-values. This means that it’s now much easier to make informed comparisons between the R-values of various sleeping pads, regardless of the manufacturer.

This standard adoption is likely to be as important for consumers as the shift that occurred when companies adopted standardized temperature ratings for sleeping bags. Before now, some companies, like Big Agnes and NEMO, never listed an R-value. Some manufacturers would just provide a temperature range for which they recommend their product’s effectiveness. And some companies’ sleeping pads would have an R-value of N/A or just not list any information about the temperature rating. Usually, this means that no testing was performed by the manufacturer, so it’s anybody’s guess as to how well the pad insulates.

But now that there’s an industry standard, many companies have begun testing their pads and updating their product descriptions to this standard. These companies include:

  • Therm-a-Rest
  • NEMO
  • REI
  • Exped
  • Sea-to-Summit
  • Big Agnes
  • Klymit


This standard adoption in the US was largely driven by REI, which requires that the sleeping pads listed for sale on its website have an ASTM F3340-18 R-Value rating.

The standard test for sleeping pads is fairly simple. In the ASTM F3340-18 test, sleeping pads pads are sandwiched between a 35ºC/95ºF hot plate on top to mimic body heat, and a cold plate that’s 5ºC/41ºF beneath to mimic the ground. Over the four-hour testing period, the energy that the hot plate uses to stay at a consistent 35ºC is measured. The less energy it takes, the more insulative the pad is, and the higher the R-value is.

This testing makes it easier for you to make informed choices and helps you select the right sleeping pad based on your needs and the specific conditions you’ll face during your outdoor adventures.


R-Values At A Glance

So what do these R-values mean? Generally, R-values run from 1 to 7, with some less-portable mattresses having an even higher R-value. The values are fairly straightforward; a pad with an R-value of 2.0 is about twice as warm as a pad with an R-value of 1.0. R-values are additive, so if you combined the 2.0 and the 1.0, it would be about the same as a pad with an R-value of 3.0. This means that you can add a summer pad to a 3-season pad for winter camping, instead of buying a new pad that’s likely thicker and heavier than the ones you already have.

Different sleeping pad R-values are appropriate for each season.

Pad R-Value Season Expected Low Temperature
1-3 Late Spring, Summer Above 35 degrees F
3-5 3-Season 5 – 35 degrees F
5+ Winter/4-Season Below 35 degrees F


Choosing A Sleeping Pad

When selecting a sleeping pad you should consider the R-value along with the weight, thickness, and type of pad. These all work together to create different degrees of functionality. All these metrics often increase together so a higher R-value sleeping pad is also thicker and heavier. This isn’t always the case though, especially for inflatable pads, so if you are planning a long hike and you are trying to save on weight, it is worth doing the research. This is especially important for ultralight backpackers!

Side sleepers and women must also make special considerations when choosing sleeping pads. If you sleep on your side then you should avoid thin inflatable sleeping pads or go for a higher R-value than you expect you need. This is because not all of your body will be in contact with the sleeping pad surface, so you won’t receive the full effects. Some sleeping pads depend on body heat to warm up and insulate you as well so the lack of body contact will inhibit that.

Women should also choose a sleeping pad with a slightly higher R-value than needed because they have less body mass than men. The lower body mass means they retain less heat and are more susceptible to hypothermia and other conditions. This also applies to children and generally for anyone who tends to have a cold body when sleeping.

Overall, you should consider the choices you make with your sleeping pad as part of a bigger picture. Your tent, sleeping bag, clothing, and sleeping pad all work together to properly insulate you from the environment. Collectively you have to consider the temperatures you might encounter, the weight you can carry, and the amount you can spend on each item.

You must also seriously consider the environment that you will be in relative to your personal preferences. Specifically, you need to think about what type of ground will you be sleeping on and how sensitive you are to the cold and other environmental conditions.

For example, if you are expecting sharp sticks and rocks the whole way, and you know you are a light sleeper then go for a thicker closed cell pad. Alternatively, if you’re looking at warm, grassy meadows and you sleep well anywhere you might just get by with the thinnest and lightest pad available.


The Dangers of the Wrong Sleeping Pad

Whenever a warm object comes into contact with something cooler, heat begins to transfer into that cooler object. When that warm object is your sleeping body and the cooler object is the ground it becomes dangerous. At best the heat transfer is minimal and you just wake up tired and sore, at worst hypothermia can set in.

Conduction of body heat into the ground is not the only way our body loses heat. A significant amount of body heat can be lost through radiation and evaporation. When radiation, evaporation, and conduction aren’t kept in check that’s when the real danger occurs. In freezing temperatures, the body can quickly lose heat faster than it is produced.

The ground will often be significantly cooler than the air around it and this is even more of a problem if the ground has frozen. Under these conditions laying down to sleep and exposing so much of your relatively warm body mass to the cold becomes a risk. The right sleeping pad can prevent an emergency by trapping your body heat above ground and in you.

Without the right sleeping pad, your body will slowly radiate and conduct heat to the colder surroundings. This might not pose an immediate risk, depending on the degree of cold, but hypothermia can set in slowly over time. It doesn’t have to be quick or extreme.


Final Verdict

Taking the time to buy the right sleeping pad with an appropriate R-value for the environment it will be used in is very worth it. As temperatures outside drop, ground temperatures will be even lower. When you lay down on that cold ground, even from within a tent, all your body heat is at risk of being slowly conducted into the ground. The right sleeping pad can prevent this.

With proper insulation helping you maintain your body heat throughout the night you can wake up refreshed and energized as opposed to weak and drained. You will also stave off the pernicious effects of hypothermia which can set in even when you don’t expect it.

Max DesMarais

Max DesMarais

Max DesMarais is the founder of hikingandfishing.com. He has a passion for the outdoors and making outdoor education and adventure more accessible. Max is a published author for various outdoor adventure, travel, and marketing websites. He is an experienced hiker, backpacker, fly fisherman, backcountry skier, trail runner, and spends his free time in the outdoors. These adventures allow him to test gear, learn new skills, and experience new places so that he can educate others. Max grew up hiking all around New Hampshire and New England. He became obsessed with the New Hampshire mountains, and the NH 48, where he guided hikes and trail runs in the White Mountains. Since moving out west, Max has continued climbed all of the Colorado 14ers, is always testing gear, learning skills, gaining experience, and building his endurance for outdoor sports. You can read more about his experience here: hikingandfishing/about