casey16•3d agoOG Member

Just read about sleeping pad R-values and had to redo my whole setup

I was browsing a hiker forum last night and saw someone mention that R-values stack when you use two pads. I always thought the foam pad under my air pad was just for insulation, not actually adding to the warmth rating. Turns out my 3.2 R-value air pad plus a 1.5 foam pad gives me about 4.7 total, not the 6.2 I assumed. I tested it on a 35 degree night in the backyard and got cold by morning, so now I'm looking at which combo to swap for colder trips. Has anyone else been confused by how R-values work with multiple pads?

2 comments

2 Comments

richard_dixon3d agoProlific Poster

Gotta watch out for that R-value math, it ain't simple addition like most people think. The air trapped between the two pads actually works as its own insulation layer, so you're really stacking three R-values not just two. A friend of mine got cold on a 20 degree night using a 4.5 pad under a 2.8 foam pad because the air gap created a cool bridge right between them. Some folks swear by putting the foam pad on top of the air pad instead to break up that heat loss path. The whole system depends on how tight the pads seal together and if any air pockets form underneath you. That 35 degree test taught you more than any chart ever could.

jennys723d ago

Man, this whole air gap thing brings back a memory. My buddy thought he was being clever by layering a cheap pool float under his sleeping pad for extra "cushioning" and he woke up shivering in the middle of the night because that thing was basically a cold sink. He spent the rest of the trip wrapped in a tarp like a baked potato.