A good night’s sleep is the difference between loving your camping adventure and never wanting to go again. Of course, your camp mattress is an integral part of how well you sleep. Bringing the right one is essential. With so many options, it can be hard to know which one you need.
In this guide, we take an in-depth look at the sleeping pad R-values and more. You’ll learn what R-values are and why they are important. We’ve included tips for finding the right thermal rating, what to consider when shopping, and information about R-value testing.
- Go with the flow – R-values measure how well sleeping pads resist heat flow from your body to the ground.
- Knowledge is power – Understanding R-value thermal ratings is critical to building an effective sleep system that will keep you comfortable and safe.
- It all depends – Which R-value you need depends on many things, including sleeping bag rating, ambient temperature, ground temperature, and your personal thermostat.
Table of Contents
R-Values: All You Need to Know
What Are R-Values?
R or resistance values are used to measure how well an object can resist the flow of heat. The term comes from the building industry, where it is used to indicate the efficacy of different types of insulation, windows, and construction materials.
When it comes to sleeping pads, R-values measure the same thing – conductive heat flow. Except in this case, it’s the heat flow from your body to the ground. In other words, this value indicates a pad’s ability to insulate. For outdoor gear, R-values usually run from 1 to 7.
As you can imagine, the thicker a pad is, or the better it insulates you, the higher the pad’s R-value. For example, summer pads have an R-value in the 1-3 range, and winter camping or 4-season pads will have a thermal rating closer to or above 7.
The scale is simple, and so is the math. Pads with an R-value of 6 are twice as warm as 3-rated pads. When stacking different sleeping pads, add their R-values together to calculate their combined rating. It is that straightforward.
Be aware these numbers do not correspond to temperature. For instance, a 3 R-value doesn’t relate to a 30°F-40°F range. The R-value is an independent rating.
Why Are R-Values Important?
R-values are important for building a sleep system that can keep you warm and safe. Heat transfer is always an important factor in the outdoors. When thinking about how to layer your clothes or which socks will keep your feet warmest, you’re thinking about how to avoid heat transfer.
Avoiding heat transfer while you are sleeping is not only essential to a good outdoor experience, but it can also be critical in survival situations. When you lie directly on the ground, your body heat moves from you into the ground and will quickly make you cold.
Sleeping pads insulate you from the cold ground. Understanding R-values allows you to find the appropriate sleeping pad for the anticipated conditions. Likewise, sleeping bag ratings are based on laboratory tests that include a sleeping pad. Your sleeping bag and pad work together to keep you warm. If you know your R-value, you can pair it with the right sleeping bag.
For example, if you have a colder-rated sleeping bag, you can get away with a lower R-value-rated bed. On the other hand, if you have a lighter sleeping bag, you might need a thicker sleeping pad.
What R-Value Do I Need?
No one can tell you exactly which R-value you need. There are so many things to consider when choosing sleeping mats, including personal preference, how you run (hot or cold), weather conditions, sleeping position, and your sleeping bag rating, to name a few.
We can provide general season ranges and lower limits for different R-values. Unless you are strapped for packing space, we recommend erring on the side of warm. A thicker pad won’t make you overheat the way the wrong sleeping bags might. Check out the general guidelines below for an idea of what you might need:
- Summer: 1-4
- 3-season/Spring and Autumn: 2-6
- 4-Season/Winter: 5-7
- Alpine/Extreme Conditions: 7+
There are many other things to consider when looking at sleeping pads. Here are a few factors that affect which R-value is right for you.
The surface where you’re camping makes a big difference. Rocks and dirt are good at stealing your body heat, especially in the winter. Believe it or not, snow is a poor conductor and will make you less cold than the ground. Either way, camping during the colder months requires a higher R-value.
Alternatively, you can use a thin closed-cell foam pad or inflatable pad under your bed for extra insulation. And don’t forget R-values are additive. Stacking pads provides more insulation. Mylar blankets that reflect heat back to you can also increase your R-value.
In a pinch, you can even use pine needles and leaves between your pad and the ground to add insulation and reduce body heat loss.
Sleeping Bag Temperature Ratings
Your sleeping bag’s temperature rating can have a big impact on what kind of insulation you need. Even with a heavy-duty sub-0°F bag, you still need something between you and the ground. A sleeping bag cannot provide thermal protection. Your body weight compresses the sleeping bag filling and renders it useless against the cold ground.
In fact, your sleeping bag won’t work as it should without a proper sleeping pad. Make sure your sleeping bag and pad complement each other. In some cases, you won’t need as thick a mattress with a lower-rated bag.
You can combine a summer pad with a warmer sleeping bag in most conditions. A winter camping pad with a lighter bag can work as well. Of course, for extreme alpine or Artic-type expeditions, pair your thickest pad with a 5-season bag.
Side sleepers might need higher R-values because their weight isn’t as evenly distributed as a back sleeper’s. If you move a lot between positions all night, try a sleeping bag with a built-in sleeve for pads. This can help keep you and your bag on the pad.
Restless sleepers might also like air pads with textured surfaces. This helps keep squirmers from sliding off their pads at night. Nothing is worse than waking up on the ground, and R-value doesn’t matter if you roll off your camp mattress.
Pad length can change which R-value you need. 3/4-length pads are good for summer adventures but don’t offer enough insulation for colder months. For ultralight adventures, short pads can help cut down on weight. Use your pack under your feet for insulation with a 3/4 pad.
Mummy-shaped or tapered pads can reduce your pack weight while offering thermal protection for your feet. Be aware that sleeping pads that come in multiple sizes all have the same R-value unless otherwise specified.
Weight and R-value go hand in hand. The higher the R-value, the heavier the pad will be. Ultralight and long-distance backpackers are known to cut ounces in the mattress department.
When weight is paramount, and you’re willing to be a little cooler at night, you can sacrifice your insulation. Just know this means you might be chillier at night. When space and weight don’t matter, we recommend a higher R-value pad.
Everybody has their personal internal thermostat. Some people are warm-blooded no matter the temperature, and others can’t warm up, even in the middle of a heatwave. Your baseline body temperature depends on age, size, and sex.
Knowing if you run hot or cold can be helpful for choosing the right R-value in a new sleeping pad. For people that never get cold, a lower value is better. For the chronically cold, go with a higher R-value, AKA a thicker sleeping pad. A good rule of thumb is to add 1 R-value for women and cold sleepers.
Which R-value you need also depends on your intended use. Are you a car camping enthusiast, backcountry enthusiast, or intent on high-elevation bivouacking and cold-weather camping? Look for an R-value that will cater to your usual use. Ultralight backpackers and car campers don’t need the same camp bed thickness.
If you don’t know where your future camping plans might take you, try something in the 2-5 range. Pads in this range will cover most of your bases and work for three-season use, including spring, summer, and the majority of fall adventures. You can always add a thin foam pad or closed-cell mattress to the stack for shoulder season outings.
In these conditions, you’re going to need a little extra thermal resistance!
What you wear to bed is an important part of your sleep system. Your pajamas can affect which thermal resistance you need. Some folks prefer to sleep in socks, long pants, and a sweatshirt when they camp. Others would rather die than wear their socks in their sleeping bags.
Those that de-layer for bedtime might need more insulation. If you always wear longjohns and a beanie in bed, you can use lower R-value sleeping pads.
Your camp shelter can help you determine which R-value you need. Tents with footprints provide more insulation than floorless tents. When you don’t put down a tarp or footprint, you’re closer to the heat-stealing ground, which means there’s more conductive heat loss.
So, if you are committed to the floorless canopy, footprint-free tent, or cowboy camping, think about getting a thicker mattress. Likewise, an enclosed tent can protect you from wind chill, meaning you might be okay with a thinner pad.
However, a tarp is not a sleeping pad replacement. A good tarp can insulate you a bit, but it cannot provide the same level of insulation as a camp mattress, even one with a low R-value.
Cost and R-value are not usually correlated. This is because ultralight camp mattresses are often pricey but don’t have a high R-value. Cost depends on material, durability, and weight more than thermal resistance. Ultralight backpackers, who count every ounce, will splurge on lightweight sleeping pads but might sacrifice warmth in the process.
When cost is a concern, stay away from ultralight sleeping pads, and opt for something cheaper with a higher R-value. Air and self-inflating pads are great middle-of-the-road options that come in a variety of sizes and thermal ratings.
Closed-cell foam pads are your cheapest option, but usually don’t exceed an R-value of 3. They can be perfect for summer camping and layering with air mattresses.
How Are Sleeping Pad R-Values Tested?
Sleeping pad manufacturers have to subject their products to standardized testing (ASTM testing) to determine R-values. This means you can compare R-values across different brands and models and know they mean the same thing.
The ASTM R-value standard test involves putting pads between two metal plates. One hot plate is set to 35°C to mimic human body temperature. The other plate is set to 5°C to represent the ground.
The pad stays there for four hours. During the four hours, researchers measure how much energy the warmer plate uses to maintain its temperature at 35°C. The more energy it takes to stay warm, the lower the thermal resistance, the R-value, of the pad. The less energy it takes, the higher the R-value.
A good night’s sleep is the difference between loving your camping adventure and never wanting to go again. Of course, your camp mattress is an integral part of how well you sleep.
We hope our guide to understanding R-values makes building the right sleeping setup a little easier, and we wish you sweet dreams on every camping trip to come.
Share any questions you have about thermal resistance in the comments, and don’t forget to share this article with your camping crew.