(Note: this review is for the older, square NeoAir Xlite. They lasted so long, we're just about to buy the new, tapered version).
Em is one of the best sleepers I've ever known. She can sleep well if the environment is noisy, if it's bright, if the ground shakes. Literarily. I woke her up a few times during small earthquakes. She only needs is to be warm, she gets cold very, very quickly. Me, on the other hand, am the exact opposite, I sleep awfully pretty much all the time, but my metabolism is very fast. Em calls me her personal furnace - you could say I'm an integral part of her sleep system.
The other two main components are the sleeping bag (there's our trusted and beloved Nunatak Dual Arc Alpinist) and the mattress. What's between your body and the ground is just as important as what's around you and the surrounding air. The ground being usually pretty hard is one thing, so some soft material is not a bad idea, but the main job of a mattress is insulation. Lofty materials, like the filling of a sleeping bag do not insulate at all when compressed – it's mostly the air between the bits of filling that insulates). This is why many "serious" sleeping bags have zero or almost zero filling at the bottom, or some are even open, like ours, and technically become a quilt.
Back in Dark Ages of our backpacking history (dark = heavy) we carried self-inflatable "Gear Guide" mattresses what were huge, weighed 4 pounds and had an R-value (explained below) of around 2. During the Age of Enlightenment, when we "enlightened" our load, I put a lot of time into finding the smallest, lightest and best insulating mattress there is.
One option was CCF (closed cell foam). These pad have huge advantages: they are very light, very cheap, insulate relatively well and chiefly, they simply can't fail. However, they are not for us. As there's nothing to deflate, so they're huge. Usually you can see them on the outside of people's packs. Our goal was not to carry any major item on the outside, and mainly, all the ones we tried were very uncomfortable.
Alas, I decided to look for regular, inflatable air mattresses. Many people are very wary of them for the (somewhat rightful) fear that they can be develop a leak easily. I spent countless nights as a kid on regular old air mattresses while camping, and yes, they were leaks sometimes, but it was never a big deal.
When researching these pads, one stood out pretty quickly: the Neoair Xlite by Thermarest, so I bought two when I found them on sale.
It's thick and insulates really well (R-3.2). The short version weighs a whopping 8 ounces and it packs down to about the size of a quart bottle. This is by far lighter, smaller and better insulating than anything else out there.
Here's the caveat: "short" means it's only 49" (119cm) long. For an average height person it comes down to about mid-thigh if measured from the top of the head. So how can you sleep well on that?
Like with many other ultralight outdoor pieces of equipment, there's a learning curve and it requires some tinkering. We tried all sorts of configurations, but after a few nights we settled on the following system and never changed it too much since: the pads begin at our shoulders, with our heads hanging off at the end. However, we make pretty big pillows that come up high enough so it's comfortable.
One of the pillows is the sack of the sleeping bag, the other is the Sea-to-Summit mini backpack we carry with us all the time. Pretty much every scrap of spare clothing goes into the pillows, and a final item is wrapped around the case to make it nicer to the touch. For me, this is usually my Mountain Hardwear down jacket, for Em it's a shirt. Of course, I have to adjust the position of the pillow a few times at night, especially when turning around, but it's a minor inconvenience.
With the pads beginning at our shoulder, they go down past my knees, for Em, almost full length. Just past the pads, we put our empty backpacks which provide adequate comfort and insulation if we want to stretch our legs.
Then there's the question of coupling (ahem, the mattresses). First, we didn't do anything, and of course they kept slipping apart. Then we constructed two silnylon straps, each about 3" wide with small pieces of Velcro sewn on them. This is very light and works relatively well, but even so, on cold nights, we stuff one of the down jackets in between/under them to cut off some of the chilly air raising from below.
This system with the Neoairs, the Nunatak and the backpacks has worked pretty well for over 100 nights in the backcountry, ranging from 60° to 15°, of course, with variations in the setup and what we were wearing. For the vast majority of nights, down to maybe 20-25°, I always sleep in my boxer shorts, a long-sleeve Capilene 2 shirt (not very warm) and no socks. Em sleeps in the equivalent of the same (well, Capilene 3 for her). That's how well the pads insulate and that's how much the sleeping bag retains our shared body heat. For winter camping we got get the slightly heavier, but better insulated version of this, the NeoAir Xtherm. Review coming soon.
They are somewhat squeaky, that's true, but it's not very bad. I wake up as soon as Em stirs anyway, but very often, she can sleep through me making minor adjustments.
The outermost layer is PVC of course, but it's textured very well, it feels OK against the naked skin and rarely gets clammy. Of course, we're trying to avoid that as much as possible.
Inflating one takes 12-13 breaths of mine. Actually, and this will sound stupid, but inflating them is one of my favorite things to do in the backcountry, especially at night. I find a stable place to stand, turn my headlamp off, and just watch the sky while inhaling slowly and exhaling into the valve.
When short of one breath full, my trick is to close the valve almost all the way, then force some more air in and fully close it while still blowing. This way I can make it as firm as I want to.
We also have our own specific set of movements of how to let the air out, fold them and roll them up, but I'm not going to get into that here. Find your way :-)
Ah, the big question. How are they doing? Well, we bought the first pair in June 2011. At the time of this writing, it's October 2015 and we're still using the same pair. I think we used them for the last time this past weekend in Mineral King, and I'm ready to get new ones.
All this time, one of them developed an obvious leak, back in 2012. During the last two nights to Mt. Whitney, I felt one of them losing air, and after coming home, we discovered a tiny hole by dipping it in water. We sealed it with a vinyl patch and it has held for three years.
In the last few months, almost at the same time, both started losing air, but at such a small rate that we don't have to re-inflate them during the night, if they are firm late in the evening, they both hold up until the morning. However, on one the internal baffle has failed in a section and it's bulging awkwardly.
It's time to retire them.
I'm not saying sleeping in a tiny tent on these mattresses and in that bag is as comfortable as a huge bed with a memory foam mattress and nice comforters in an air conditioned or heated room. How could it be? I can still say I had better nights sleeping in the tent then in my bed in the city.
The Neoair Xlite is tiny, very durable, the lightest there is, and as comfortable as it gets. If used properly it not only gets you through the night, you can wake up feeling rested.
It's a number to indicate an insulator's resistance against heat loss. The higher the number, the better the insulation. If you're interested in the details, here's the Wikipedia article.
For our purposes, it's enough to know that three-season mattresses are usually in the 2.5-3.5 range, winter mattresses in the 5-7 range.