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R value measures the thermal value, better known as the prevention of heat loss. Essentially the higher the R value the greater the insulating power.
There are different types of sleeping pads and each style has a different R value. Choosing the right sleeping pad is important as having the wrong R value will allow cold to creep up from the ground and lead to an uncomfortable nights sleep, even though there is enough of a pad (just not enough insulation).
Different Types and Associated R Values
There are a number of different kinds of sleeping pads, generally different material pads have R values that fall into a certain range. Let’s now look at the different styles and the associated R value.
Closed Cell Foam – These are generally the type of pad most people start with. They are relatively durable compared to air pads (that could potentially pop). They are easy to replace as many stores have them.
Closed cell foam generally has an R value of around 2 thru 2.5. Therma-Rest Ridgerest Solar is one of the highest rated closed cell foam sleeping pads on the market with a 3.5 R value rating.
Self-Inflating - (uninsulated) and Inflatable - These are pads that utilize air to inflate and do not have insulation. They are either self-inflating (no need to blow air into them), or inflatable where you need to inflate them with a baffle or by blowing into them.
These sleeping pads are generally a summer season sleeping pad and have an R value of 0 thru 1. You would not want to use these in the winter and likely not in the fall either depending on the climate where you are.
Insulated (Air) – These are pads that are self-inflating or require air to inflate; generally, R values fall between 3 thru 6. These you can use year around accounting for your climate.
R Value Ranges
How Do They Keep You Warm?
If you were to lay directly on the ground your body would lose heat through conduction. Being elevated off of the ground will avoid conduction. Unfortunately, this leads to another way to lose heat, convection. To prevent heat loss through convection (at least those pads that are insulated) have some form of insulation within the pad to stop heat loss due to convection.
What Insulating Materials Are Used In Sleeping Pads and Which is Best?
A number of materials are used in production and often many are combined to provide what manufacturers think is the best combination to keep you warm. Foam is used in many closed cell pads. This stops air flow and naturally provides an R value.
Some use reflective materials with the theory that these materials will reflect a portion of the user’s body heat back up to the user, a similar concept to a survival space blanket.
Lastly, down or synthetic materials are used to trap body heat, prevent air flow and provide insulation.
These materials combined with baffles, ridges and other manufacturing techniques will give you a warmer night’s sleep when used with the correct sleep gear and clothing.
Other Factors Impact Sleeping Comfort
There are a number of other factors that determine sleeping comfort in addition to sleeping pads. While I cannot cover a definitive guide here I will provide some high-level tips and will be sure to cover this in greater depth in another article.
How You Dress – Before going to sleep you should change out of the clothes you wore during the day. During the day as you are more active you sweat and this moisture gets trapped in your clothes. When you go to sleep and are less active if you do not change this moisture can cause you to have a miserable night’s sleep.
Before getting into your sleeping bag, remove all of your clothes and hang them somewhere so they can continue to dry overnight. Put fresh clothes on according to the conditions you are sleeping in.
Personally, I put on some type of base layer (silk weight for warmer weather or heavier weight for colder weather).
I also put on a fresh pair of wool socks (adjust thickness for weather conditions).
Lastly, I will put something on my head, in the winter it is often a wool or fleece hat, in the warmer months it is often just a bandana or some other light weight material (being bald doesn’t help retain heat like those with a full head of hair).
Other Sleeping Gear – Having a quality sleeping pad, but other sub-optimal sleeping gear isn’t ideal. You should have a sleeping bag that is aligned to the temperature you expect to encounter. Generally, I recommend adding 10 degrees to the stated sleeping bag rating.
You should also consider using a sleeping bag liner. This not only will help keep your sleeping bag clean but it will add modest amounts warmth to your sleep setup.
What Are Some Ways To Increase R-Value (without buying another pad)?
Budgets can be tight and sleeping pads can be expensive so I fully understand you may not want to purchase a new high R value pad. There are some things you can do to improve the R value of your sleeping pad.
You will have to experiment and see what works best for you.
The easiest way is to double up pads. I have an air pad that had an R value of 2.5. Often in the winter I will get a foam pad (very inexpensive) and place that pad underneath my air pad. Not only does it add to the R value it will also protect the air pad from sharp sticks, rocks and other things that may puncture your pad.
I have also seen people take a heavy wool blanket and place that on top of the pad, this seems to work well too.
Lastly, in a pinch and based on what season you are in you can take leaf litter from the forest floor and make a pile about 3 – 4 feet high and put your pad over this. Just be careful to clean any sharp sticks and any other items that may puncture your sleeping pad. Generally, this is only recommended if you are using a foam sleeping pad.
How is R-Value Tested?
Unfortunately, there is not an industry wide standard on how companies must test the rating. Some companies will use the pad in a variety of conditions and come up with a relative rating, while others will simply estimate a value and run with it.
This isn’t ideal and it makes it hard to compare across different brands of sleeping pads. It is best to buy a respected brand that has plenty of reviews so you get an idea from people who have actually used the pad to give an opinion on the accuracy of the rating.
You should also test the pad out yourself close to home or near your vehicle where if the pad was grossly over estimated you can bail or get a backup pad to use. The last thing you want to do is go out on a multiple mile hike into the woods and have a pad that isn’t working from an insulation standpoint.
Winter vs Summer
For a winter sleeping pad the value should be around 4 or 5. This is the minimum you should have to have a comfortable night’s sleep. In extreme cold you should enhance the pad if you are on the lower end.
For summer time use many people use a sleeping pad without an insulation (just air) or a single foam pad. This is usually fine because you likely won’t notice the lack of insulation. Using a higher R value pad won’t hurt although if you are a warm sleeper you may wake up a little warm throughout the night.
At the end of the day you can’t go wrong, just test your gear, have backup plans and error on the side of caution until you have some real-world tests with all of your sleep gear. Never 100% trust the companies’ ratings.
This will ensure you do not spend cold nights out on the trail or at camp.