Rating: 3 / 5
This is a preliminary review that will be updated later this spring/summer when I get more experience with the sleeping pad outdoors. I will post what I know so far in order to help answer people's questions about the pad.
The pad weighs 251 g, the hand pump 36 g, and the patch kit 11 g. After some testing, I found it best to inflate by mouth only. When inflated to higher pressure, the pad became too hard and lumpy, and numb spots would form on my back when I slept on my side. (Note: I am 190 cm tall and 75 kg, so tall and thin).
The pad is narrow. When I lie on my back my elbows and lower arms fall off the side of the pad. In my case that's not a problem (see below). It is also shorter than me, so about 8 cm of my feet are hanging off the bottom end when I align the rest of my body correctly with the pad. Again, for me this is not a problem (see below).
I am a quilt sleeper, so getting this pad was a bit of a gamble. But I've found a way to make it work very well for me — at least so it seems for now, after 4 nights of testing on the balcony at temperatures from 6 to 10 degrees C.
The pad alone is insulation enough for temperatures down to about 12 C when wearing a Marmot Cocona PowerDry layer under a quilt (which has an open back). Putting a 1/4'' GG evazote pad underneath lowers that limit a few degrees, perhaps to 9-10 C. But ultimately I found the most comfortable solution to be placing the second pad on top of the Inertia X. My 1/4'' thick pad weighs 120 g, is 55 cm wide and about 165 cm long (bought from the Gossamer Gear site and cut in half). With this pad on top the comfort temperature is lowered to about 3-5 C. To get lower than that, I will fold the GG pad and use it as a torso pad, placing the back padding from my ULA Ohm under my legs. Or, I'll put the back pad on top of the GG pad underneath my torso.
In any case, an effective sub-zero C pad system with the Inertia X weighs about 350 to 400 g (151 g + 11 g patch kit + 100-140 g additional pads). That's 130 g more than my PCT thru-hike pad set, consisting of three different GG pads. Is it worth it?
My impression so far is, "Yes" — unless the Inertia X develops a puncture that can't be fixed. I've had two inflatables already — a Thermarest short and a BMW Torsolite — that disappointed me by developing incurable microleaks. However, Ron from MLD stated that he had not heard of puncture problems with the Inertia X, so I decided to give inflatable pads "one more try."
The pad combo described above provides bed-like comfort, and I have been sleeping very well on the balcony on both my side and back. The lumpiness of the Inertia X pad is lessened by the additional 1/4'' pad.
An unexpected advantage of the Inertia X over other inflatables is that it has no lower back area to push up into your lower back when your buttocks push down into the pad. With the Torsolite, I often would get a sore back when sleeping for hours on my back. I didn't realize what the problem was until I did some reading on the form and found that it has to do with how inflatable pads equalize the pressure under the weight of a human body. With the Inertia X, you feel like you're on a firm matress — i.e., pushing down on the matress in one place (buttocks) doesn't make the matress push up with greater strength in another (lower back).
With the second pad on top, it is actually comfortable to have my lower arms hang over the side, since there is a bit of GG pad underneath them. For this purpose a 60 cm wide pad would be better than 55 cm. I can also stick something under the balls of my feet to keep them from getting cold (so far not a problem).
Sleeping on my side is also a pleasure. Here, the pad's narrowness and insufficient length fit my sleeping profile perfectly. The only possible downside I've noticed is that the GG pad squeaks against the Inertia X when I make major body movements. But it grips it well enough that I don't have to adjust it during the night.
When used together with the GG pad, the Inertia X seems very comfortable and functional. Inflation, deflation, and storage are quick and easy (in my case I leave it in the bivy sack with the quilt and store it all together to save time). Compared to my lighter PCT pad combo, this new set cuts down on bulk and is more comfortable. Given the weight difference, if the new setup provides 8-10 minutes more quality sleep per night, then it's worth it, because I will actually cover more ground then while carrying slightly lighter gear.
I would not consider shortening the Inertia X pad because of its considerable thickness. In my experience, significant height differences between torso and legs result in at least some amount of lost sleep or physical discomfort. Then you have to spend more time in camp arranging your bed to put something soft under your legs. Not worth it for a 100 g weight savings, IMO.
I expect to use the Inertia X during an all-summer backpacking trip through Europe and will update this review later.
FINAL REVIEW AFTER 100+ DAYS OF SLEEP
The first puncture occured on about day 48, the second 24 days later, third — 12 days later, etc. All the failures were in corners on the bottom of the pad, strongly suggesting a failure of the materials rather than actual punctures. I had about 6 such failures over 100 days. Each time I was able to fix them later, but what a pain! Luckily, I was carrying a backup 100 g GG pad, otherwise I would have had a few very, very miserable nights rather than just merely miserable.
The pad is nice enough and very comfy as I wrote above, but my puncture tolerance is about 1 in 100 days. This will not do. Actually, after the 6th puncture I patched up all the corners in the area where the failures were occurring. Since then it's been fine. But MAN!
UPDATE MAY 2013
I have finally written Klymit about this defect and will be getting a replacement pad for free from them. This will probably make me update my rating to 4 or 5 since I otherwise like the pad.