I've been a Boy Scout for seven years now, and as I'm moving from high school to college I'd like to get into solo backpacking. I live in the lower peninsula of the state of Michigan. I don't foresee camping in anything under 10°F (-12°C). To camp four seasons, what would be a good R value for my sleeping pad?
My 2 Cents:
Winter camping requires two pads, one inflatable and one foam. The reason for this is that not having any pad at all looses a lot of heat into the ground if you are camping on snow. Even the warmest bag will be uncomfortable without a pad camping on snow. While inflatable pads are really nice, they all eventually fail, particularly in the presence of crampons.
You can survive the night with any of the standard selection of foam pads. A good inflatable pad plus foam pad will extend the range of your sleeping bag and provide comfort vs survival. In my experience people underestimate how much heat gets lost into the ground.
The other advantage of having a foam pad is that you can use it quickly during the day during rest stops. Being able to sit without losing heat makes a big difference as the day goes on.
Managing two pads is kind of a pain, those large elastic straps with the Velcro ends help in keeping them both under you.
It looks like there is not a consensus on what the minimum R value should be, but that the higher the R value the better. It will also depend on how you sleep and what your comfort level is.
If it would be possible to borrow one to try it out before going I would suggest doing that. Its worth trying the pads out in advance where you won't freeze to death if the pad turns out to not be warm enough.
Another useful bit of knowledge is that you can generally draw the line between three-season and winter mattresses at an approximate R-value of 3.0. We also think that if a mattress is to supply any reliable amount of warmth, it should have an R-value of at least 1.5. Any less and you could basically be sleeping on a heat sink, which can continually drain warmth from your body, making for a pretty grim night.
Pros: Air pads are incredibly comfortable and lightweight and the most compact type of pad when packed. Most are designed for backpacking or camping in warm conditions (about 3 R-value) while others are designed with additional insulation for four-season use. You can customize the firmness of the mattress by releasing some air from the valve while you’re lying on it.
In sub-zero temperatures most people (varies according to the individual) require an R-Value of 4 or more in order to feel comfortable. In milder conditions, sleeping mats with R-Values of 2 to 3 generally suffice for most hikers.
In general, sleeping pads with R-values of 0-2 will only be good for warm weather trips. R-values of 2-4 are good for most 3-season backpacking conditions. R-values of 4-6 are good when the temperature drops around or below freezing. You’ll likely want a pad (or combine a foam and air pad) with 5+ R-value if you’re winter backpacking and you’ll be sleeping on snow.
There are a lot of factors that determine what R value you will need. While the low temperature might be 10°F (-12°C), the ground could be substantially warmer (or potentially colder). The temperature of the surface you are sleeping on is much more important than the air temperature. It also matters how well the surface conducts heat; sleeping in a hammock (or a raised lean-too shelter) is going to be much colder than on snow.
Another big factor is your sleeping position. If sleep on your side, you have a lot less contact with the ground and the sleeping bag is going to matter more. A stomach sleeper will lose much more heat through the pad and the bag will be less important. If you use a quilt instead of a sleeping bag, that will also influence heat lose through the pad. Finally, if you are a warm sleeper, you will need less of a pad than if you sleep cold.
All that said, most people will be comfortable in most conditions with a low of 10°F (-12°C) with an R value in the 3-4 range. That said, there is no reason you cannot use multiple pads (e.g., an inflatable pad and a closed cell foam pad) to get you the total R-value you want.