R-Value: What Is It?

What is R-value? What does it mean? And what should I choose?

What does it mean?

Technically, what we call R-value is a unit of measurement / numerical value that describes the thermal resistance or resistance value in English.
Simply put in Danish; the insulation ability.
The higher the number, the better the R-value, which equals better insulation ability.

R-value is not only used to determine how well a sleeping pad insulates you from the cold. Many products such as insulation for your house, doors, windows, concrete, and I could go on, have an R-value.
Now you might be thinking; I have never seen anything about R-value on the insulation I bought for the attic, and no, it doesn’t say that.
In Denmark, we have other terms, and there are many different names for it, including lambda and U-values used in insulation materials.
Everyone uses an 'R-value' with their own little twist and way of measuring it, but it’s still the same – namely the ability to insulate.

Should I care about how the R-value is determined?

Yes, you should.
The R-value must be made and approved according to a standard called ASTM F3340-18.
This standard helps make it easy for you to choose the right sleeping pad the first time.
If the sleeping pad is tested according to ASTM F3340-18 standard, you don’t need to think any further, as you can safely rely on the R-value stated.

In the past, manufacturers each had their own 'standard' for determining the R-value, which made it a bit like the wild west, as they did not calculate the R-value according to the same principles, and therefore you couldn’t be sure that a sleeping pad with an R-value of, for example, 6, would protect you from the cold underneath in winter the same way as another sleeping pad with an R-value of 6.

So if you want to be as sure as possible, look for which standard the manufacturer tests their R-value according to, and if it is ASTM F3340-18, then you have a really good basis for comparison between brands.
Of course, this does not mean that if a sleeping pad is not tested according to the ASTM F3340-18 standard, it is not a great sleeping pad, because it can be. The ASTM F3340-18 standard just makes it more straightforward and accurate.

If you want to know more about the new ASTM F3340-18 standard, read more here.
 
Should I care about what R-value my sleeping pad has?

Both yes and no

No
If you only plan to go on adventures in nature during the summer, then no, it doesn’t matter that much.
One might be tempted to say yes, R-value also makes sense in summer, as the Danish summer, as we all know it, can be unpredictable, but it typically doesn’t get so cold that you can’t keep warm, so it matters very little there.

Yes
If you want to go on adventures year-round, also in the transition periods between spring-summer and summer-autumn, in winter, etc., or for example are going on a trip abroad where temperatures fluctuate much more than here in Denmark, then it matters a lot.
If you have spent a whole night freezing, your desire and energy for a new day are much more limited.

Therefore, it is especially important to know about R-value when you have higher demands for your sleeping pad, as the seasons of the year or the place you are in the world offer different temperatures, which also means there is a need for different sleeping pads with different R-values.

The 4 seasons

R-values vs. seasons and thus temperatures can roughly be divided according to this rule set:

R1 - R2 = Summer

R2 - R4 = 3 seasons (Spring, Summer, Autumn)

R4 - R6 = All seasons including winter

R6 - Up = Extremely cold

Foam pad or air pad? Should I be aware of anything?

Basically, there is no difference if we talk about R-value.
They are tested according to the same standard, if they are of course tested according to ASTM F3340-18 standard.
But comfort-wise, there is a lot to gain, if you ask us.

Here in the shop, we have a foam sleeping pad from Therm-a-Rest called MondoKing which has an R-value of a full 7. Here you get the best comfort possible, with a weight of XXLarge at 2.5 kg.
Foam sleeping pads usually offer a higher degree of comfort than air sleeping pads.
On the other side, we have the air pad NeoAir XTherm which has an R-value of 6.9 and a weight of Large - 0.57 kg, so about the same R-value but less weight and bulk.

Both sleeping pads have the same R-value as mentioned, but the big difference can be in weight, comfort, and price.
Foam sleeping pads are often cheap, which is also a factor in choosing the right sleeping pad with the right R-value.
So you should decide what matters most to you once the R-value is set, based on your needs.
Price, weight, and comfort, that’s what you should think about here.

Now I have found a sleeping pad with the right R-value, is that it?
Both yes and no...
At least you have found a sleeping pad that fits the season you want to sleep outdoors in, and that is more than halfway there.

Most of the cold comes from below, but the sleeping bag also plays an important role in getting a good night’s sleep.
Just as sleeping pads have an R-value that tells which season they are suitable for, sleeping bags have a comfort temperature. This comfort temperature should of course match the season’s temperatures you want to sleep outdoors in, and the R-value of your sleeping pad, to ensure the best nights with the most energy for the next day.
I’m a cold person, which R-value should I choose?
If you are a cold person like me, go one season lower in temperature; you can always unzip the sleeping bag a bit. You are going on an adventure, and you do that best with energy and good spirits 🏕 😊

An important thing about R-values and values in general.
As humans, we can easily get fixated on numbers and values.
Just like a car rated to drive 20 km per liter but only manages 15-17 on the highway when we drive it, remember that when they test and state R-values and comfort temperatures, it is always under the same “test” conditions.
They do not take into account whether it is stormy, windy, or what the chill factor is in those cases.
The chill factor has a big impact on all the gear that needs to keep you warm.
Wind can drastically lower the temperature. In Denmark, we have an average wind speed of about 7 m/s, which means that at 0°C and wind at 7 m/s, it feels like -12°C, so it can have a big impact and should be considered.
The conclusion is that you should always choose a sleeping pad with a slightly higher R-value if you are unsure whether it is high enough.

R-value and temperature chart