Sleeping pads provide comfort which can enable a good night of sleep. Waking up in the morning feeling worse than when you went to bed is no fun. Some people can sleep on the bare ground or maybe 1/8″ foam pads for some insulation. I wish I could do that for the weight and volumes savings, but I can’t. When I have tried more minimalist padding, not only have I not slept well, but in some cases I woke up with new aches which continues for several days (my hips in particular). I have heard people assert that after a few days on the trail you will be able to sleep without a lot of padding because you have worn yourself out. This is not the case in my personal experience.
There is an even more important reason to consider taking some sort of pad… and that’s to stay warm. Sleeping bags insulation is compressed by your body weight which means that it provides almost no insulation. If you don’t have a pad, your body will try to warm what’s below you. If the air temperature is high but the ground is cool, this might be nice.. but in most conditions you want insulation below you. The amount of insulation you need will vary depending on the air temperature, ground temperature, and what sort of “ground” you are sleeping on. For example, if you are in the mountains, sleeping on a large chunk of granite, you will find that the rock is a very effective heat sink, while if you are in a pine forest with lots of needles and soft earth below you, you need little or no insulation because the needles are taking care of you. Also note that sleeping on your side means that there is less surface area to insulate from below.. this means that side sleepers need less under insulation. Since different people require different amounts of insulation, I think it is most useful to talk about the “R” values of pads rather than what temperature a pad is good down to. Below are a list of full size pads sorted by warmth / weight: My antidotal experience is that R2.5 is good down to around 30F, R4 is good down to around 20F, and R6.5 has been good down to around 0F as a slide sleeper. This page used to have a table of mats and their R values, but it is out of date. It seem that the sectionhiker website has a much more up-to-date sleeping pad r-value table
No matter what type of pad you select you need to decide the shape and length of the pad. Personally I like pads which are mummy shaped, but full length. Except in the cold weather, when you need maximum insulation, many people like 3/4 length pad. Most people don’t put a lot of weight on their lower legs when they sleep so there is no need for the extra weight of a long pad. Some people use torso sized pads to save even more weight.
NOTE: If you use a pad which has air in it (air mattress or self-inflating) remember to lets some air out if the pad will be spending the day in a hot tent. Air expands as it gets warmer. I know several people who have damaged their pads by leaving them sealed and fully inflated at the beginning of a hot day.
I use a Therm-a-Rest NeoAir for three season trips. It’s good by itself to 35F and down to 20F combined with the torso length pad from my backpack. I was able to sleep on my side down to 25F with just the NeoAir, but if I laid of my back or stomach it was clean the pad was not warm enough. In colder conditions I combine either the NeoAir with a full length foam pad. If I did a lot more snow camping I would pick up a down insulated air mattress.
Good quality backpacking air mattresses are lighter and more compact than self inflating pads for equivalent comfort / thickness. Of course if your air mattress is punctured, you have no padding, where a self inflating pad has at least a bit of padding. On the other hand, you can use them as rafts when crossing rivers.
In warmer conditions un-insulated air mattresses can work well. On top of dirt or natural materials plan air mattresses can be used down to 35-40F with reasonable comfort… some people might be able to push them down to 30F. I have found that un-insulated air mattresses aren’t sufficiently insulated on top of rock or snow when the air temperature is below around 50F.
In colder weather a down or synthetic filled air mattresses are ideal, providing comfort and nearly unbeatable warmth/weight ratio insulation. For most people I recommend synthetic filled air mattresses. They weight slightly more than self inflating pads, but they are warmer, pack smaller, and I think are more comfortable. The lightest way get get an air mattress is to use balloons such as the the commercial balloonbed (my review) or make your own cheer-stick pad or a ultra-light poly-tube air mattress.
These days, most foam pads are closed-cell foam because they don’t soak up water, low cost, durability, and provide decent insulation. Ultralight backpackers often like to use foam pads because they can become part of the suspension system for frameless backpacks and they can be trimmed down to save weight. In the winter, foam pads are often used during the day: as standing pads to help keep feet warm, or sitting pads which help keep the user warm and dry. The cheapest form are the “blue pads” which you can find almost anywhere (from WalMart to REI) which cost less than $10. Ultra-light packers often trim this pads down to so that it is only as large as their torso or purchase torso size pads. Slightly more comfortable is Cascade Designs’ RidgeRest. Cascade Design also makes the convenient folding Z-rest which has the unfortunate tendency to wear out with just moderate use. I think the best foam pad are made from Evazote such as those sold by Gossamer Gear.
When I first starting backpacking in the 1970s self inflating pads from therm-a-rest were the most comfortable pad other than the Warmlite DAM which were extremely uncommon. These days I generally recommend spending the extra money to get one of the better air mattresses, or go with the significantly cheaper and more durable close cell foam pad.
Many people find hammocks, especially asymmetrical designs that provide an almost flat sleeping surface to be very comfortable. [I am not one of these people… I don’t like sleeping in hammocks.] When you are worried about ground water, what could be better than being suspended several feet above what concerns you. See my hammocks post for more information.
One of the most common approaches is to place extra clothing (which is pretty soft) into your sleeping bag stuff sack. The downside of this is that the stuff sacks might not be the most comfortable thing against your face. Therm-a-rest, REI, and Sea to Summit makes stuff sacks which have a light fleece sewn into them which can be more comfortable than a nylon only stuff sack. Some people bring inflatable pillows.
A cheap closed cell foam pad. The “blue” pads can be found many places for less than $10.