How do Sleeping Pads Keep You Warm?
A sleeping pad serves two functions: (1) to provide comfort and (2) to keep your body warm (most important aspect).
When a person sleeps directly on the ground, their body heat is zapped from them (known as convective heat loss). The heat loss is noticeable as your environment gets colder. Have you ever feel cold when camping in early spring even though your sleeping bag is rated for temperatures in the 20’s?
You feel cold because your body compresses the sleeping bag and thus reducing its effectiveness. A sleeping pad insulates your body from the ground. The pad reduces heat loss to the ground and helps your sleeping bag to keep you warm during the night.
This concept serves the same purpose as insulation for your home. As you provide more separation from nature, the better you can control your environment.
Sleeping Pad R-Values: What do they mean?
The “R-Value” is a method for rating thermal resistance. It measures how good a pad protects against heat loss (the higher the value, the better). The rating system is borrowed from the home insulation industry.
Be aware that different sleeping pad manufacturers determine this value differently. So a pad with an R-value of 4 (from company A) may not be the same as one from company B (R-value of 4). There is an effort to standardize how this value is calculated (projected to happen in 2020).
Recommend for use during the summer season. Provides minimal protection against convective heat loss.
Recommended for use during the 3-season (spring, summer, and fall). Provides better protection against convective heat loss.
Recommended for use during the winter season. Provides better protection against heat loss than a 3-season pad.
Recommended for use when the winter season is a little colder than usual. Provides better heat loss protection than level 3 ratings.
Ideal for frigid environments. Provides maximum protection against convective heat loss.
Will Stacking Pads Provide Extra Warmth?
Just like a sleeping bag, a high “R-Value” sleeping pad is bigger than a lower-rated one. If you are backpacking, the extra weight may prevent you from bringing the pad you need.
But here is some good news: you do not need to own a different sleeping pad for every season. Why might you ask? To increase the overall R-value of your sleeping system, add the R-value of each pad in the stack together.
For example, you usually only go camping during spring, summer, or fall. So, you decide to purchase an inflatable mattress with an R-value of 3.
Then you get invited on a camping trip to the Alps. You research the location and find that temperatures get uncomfortable at night. Instead of purchasing an expensive new pad just for this trip, you can procure a less costly closed-cell foam mattress with an R-value of 2 and lay it below your go-to 3-season pad. Now you have the equivalent of a new mattress with an R-value of 5.