Apparently you just open a valve and it inflates, how?
I could be wrong about this, but I don’t think they “inflate” in the same way a balloon is inflated.
When you roll up the mat, you’re squeezing out the air. When you unroll the mat and open the valve, the structural rigidity of the mat opens a space (or gap) between the mat’s top side and bottom side. When this happens, it creates a weak vacuum, and air rushes in (through the valve) to fill the space. The air stops entering when the pressure in the gap equals the outside pressure. You then close the valve. The structural rigidity of the mat, in combination with closed air space in the gap, makes for a nice cushion.
To expand on what Crafter_Man said…
The inside of the mat is filled with “foam rubber”. (Speaking generically, not technically.) When you roll the mat up, you not only force out the air but you also compress the foam. When you close the valve, the foam cannot expand because it’s in a relative vacuum. When you open the valve the foam expands, drawing air in through the valve.
Oh, so there’s foam inside! That makes more sense, as it would be a bit tricky to design a mat with enough structural rigidity to create a 100% air gap.
To expand on what Johnny L.A. said…
The mats employ open cell foam, which means that the airpockets that make up the foam are open at the surface, and connected to all the airpockets inside the foam. Closed cell foams are much more difficult to compress, as you must compress the air within them, rather than simply expell it.
You would only use one if you were HIKING to a campsite. They are 1 step above sleeping on the bare ground. Get an inflateable if you don’t have to carry it far (said the middle-aged man).
Sage advice. Thanks. Also thanks for the other answers, I never thought it might be foam in there. I figured it was some sort of vacuum thing, just not quite sure.
Speaking from experience they are actually a couple of steps above sleeping on the ground. Those thin strips of dense foam that roll up small enough to sit on top of your pack are one step from sleeping on the ground. Unfortunately inflateable mattresses (airbeds) get very cold when it’s cold, and very hot when it’s hot, ie they have very poor insulation.
From personally experience (2 weeks ago) I agree. You have to bring the CORRECT temperature sleeping bag. A 55 deg night on an air mattress is a chilling experience unless you have a 35 deg sleeping bag or better. I would use a cot but I haven’t found any that really like.
We used an airbed for a few days in the (tropical) north of Australia. As you say, being cold is easily fixed by using a sleeping bag. Being hot, however, is not fixable and is certainly not conducive to sleeping. Arggh, they were the worst nights sleep I’ve ever had, lying there, drenched in sweat, try move around and find a cool bit on the bed.
As someone who has been camping for many years, the Therm-a-Rest style open cell foam pads are a godsend. They are much more comfortable than the older closed cell Ensolite style pads. Granted, they are slightly heavier but the increased comfort is well worth the weight.
They come in a variety of thicknesses, from Ultralight to ones intended only for car camping. I own two, one fullsized for car camping comfort and a 3/4 length for backpacking. In winter, I carry a closed cell and an open cell for insulation from the snow.
I have noticed that as the passage of years increases, my camping pad has as well. In my teens, a beat-up Ensolite pad was all I needed. In my 20s, I used a ThermaRest pad. In my 30s, I switched to an air-mattress, with the ThermaRest on top. Now, in my 40s, I don’t bother with any of that. We car-camp most of the time, so I bought us an inflatable queen-size bed!
And I don’t feel guilty at all!