One of the best ways to sleep comfortably while camping during cooler conditions is by using a sleeping pad with a suitable R-value insulation rating.
But what exactly is an “R-value”? How is insulation measured? And what R-value rating is good for a camping sleeping pad?
Well, don’t fret. All is explained below, so you can make an informed decision when selecting the most suitable sleeping pad for you.
Article Contents:
- How Does a Sleeping Pad Keep You Warm?
- What Does R-Value Mean?
- How is R-Value Measured?
- R-Value Sleeping Pad Chart
- What R-Value is Good for A Sleeping Pad?
Pro-tip: Looking for help choosing the best sleeping pad for your next camping adventure? Check out my comprehensive article Camping Sleeping Pads: Ultimate Buyer’s Guide.
How Does a Sleeping Pad Keep You Warm?
A camping sleeping pad is designed to do two things:
- Keep your body supported whilst on the ground
- Insulate your body from the ground
Both are very important from a comfort perspective, but the latter’s main purpose is to keep you warm.
Insulation Physics Explained
From a thermodynamics stance, heat energy flows from areas of hot to cold. Heat energy transfer can occur through:
- Convection – through the air from the surface
- Conduction – through the material itself or via direct contact
Radiation – through heat waves between objects that aren’t in contact, i.e., the sun (doesn’t play a significant role when it comes to sleeping pads)
For this reason, if you lay directly on the ground, the heat energy your body produces will be transferred into the ground via conduction.
Now, the rate of heat transfer and heat loss can be quite significant, especially if there’s a large temperature difference between your body and the ground.
- To prevent conductive heat energy transfer, you need to create a barrier between your body and the ground made from something “anti-conductive”.
Air is actually a great barrier because it doesn’t conduct heat very well. But, unless you can levitate, you’ll need some sort of material that captures air to create that barrier.
This is why homes have double pane glass with air in between the panes, insulated cups have double walls because the gap between them has air (or a vacuum), sleeping foam pads have tons of micro bubbles and air filled sleeping pads are filled with…well, air!
What Does R-Value Mean?
The insulating performance of a sleeping pad, in other words, how well it prevents conductive heat energy transfer, is measured as its R-value.
You might have come across this term, but what does R-value actually mean?
- R-Value is a standard measurement of the thermal properties of an insulating material.
- The R-Value is the material’s resistance to conductive heat flow and is dependent on the thickness and type of material.
- The greater the R-value, the greater the insulating capacity and the slower the rate at which heat energy is transferred.
This means in order to slow down and prevent loosing your body heat into the ground, using a sleeping pad with a high R-Value will do the trick.
How is R-Value Measured?
To measure R-value for any material, you need to know two things. The thickness of the material and the conductivity of that material.
The formula for R-value is just thickness divided by conductivity, written out as:
R-value = T/k
where:
- T is the thickness of the material between the hot side and the cold side, measured in meters.
- k is the thermal conductivity of the material, measured in Watts per meter per Kelvin (W/mK).
Thermal conductivity for different materials are usually measured experimentally. However, both foam and non-foam sleeping pads utilize the thermal property of air for insulation.
- Closed-cell polyethylene foam sleeping pads typically have a thermal conductivity of 0.026 W/mK. [Reference]
- For comparison, air filled sleeping pads have a thermal conductivity of 0.024 W/mK. [Reference]
Therefore, if the thermal conductivity is the same between two materials, manufacturers would need to make the material thicker to increase its R-value insulation performance.
R-Value Sleeping Pad Chart
In the table below, I’ve listed the R-value of several popular camping sleeping pads.
Here are a few things to consider as you look at all the information:
- The thicker the pad, the higher the R-value.
- The thicker the pad, the more it weighs and the larger it packs down.
- Self-inflating means foam is used inside.
- Ultra-light pads are air only.
- Foam provides more cushion and support than just air.
| Sleeping Pad | Insulation R-Value | Cost (USD) | Weight (kg) | Thickness (inches) | Type |
|---|---|---|---|---|---|
|
7.3 |
$240 |
0.44 |
3 |
air |
|
|
5.6 |
$165 |
2.44 |
3 |
foam/air |
|
|
4.7 |
$45 |
1.25 |
1.5 |
air |
|
|
4.5 |
$210 |
0.37 |
3 |
air |
|
|
4.1 |
$170 |
0.97 |
3 |
foam/air |
|
|
4.0 |
$230 |
0.85 |
2.5 |
air |
|
|
3.2 |
$125 |
0.65 |
1.5 |
foam/air |
|
|
4.0 |
$120 |
0.65 |
3.5 |
foam/air |
|
|
2 |
$48 |
0.41 |
0.75 |
foam |
What R-Value is Good for A Sleeping Pad?
Now that you know what R-value is, how it’s measured and the insulation rating for different sleeping pads, which R-value should you get for yourself?
For one thing, you should factor in R-value, as well as cost, comfort and portability, when you purchase a sleeping pad.
Personally, we use the Therm-a-Rest Prolite Plus because it balances weight, cost and insulation performance. It is important to note that we don’t do any winter camping and mostly partake in backcountry camping.
Summer Camping
For summer camping, you don’t need a high R-value sleeping pad since the ground and air temperature difference isn’t large.
I would recommend a sleeping pad with an R-value insulation rating between 2.5 and 3.5 for summer camping.
Spring and Fall Camping
For fall and spring camping, you would want a sleeping pad with a higher R-value, since the ground will be a lot colder.
I would recommend a sleeping pad with an R-value insulation rating of 4 or greater for spring and fall camping.
Winter Camping
During the winter, the ground is more or less frozen, so you should look to minimize the amount of heat loss by using the highest insulation capacity you can get your hands on.
I would recommend a sleeping pad with an R-value insulation rating of at least 5.5.
Pro-tip: Depending on the type of trip you’re doing; you may want to consider using a camping cot for winter camping. A camping cot ensures you’re supported and completely off the ground.
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