looking for one that [is].
Light,
Packs away Small,
reliable,
Warm .
Oh, dear; I'm going to weigh in here with a view based on my personal experience* and say that when it comes to pads, I've often found "light" also means "cold" or at least "not warm".
Assuming the covers are of similar weight, what makes a pad warm is the insulation/isolation it provides from the cold ground. I've tried a number of light pads, and have always returned to my heavier Nemo Tuo Standard with separate, dual chambers of solid and cross-cored foam that provide a real barrier to downward loss of my body heat. I have a Thermarest ProLite Regular that is a lovely pad...but by inner volume, the thing is half air when you hold it up to the light. That's why it is a bit less than half the weight of the Nemo Tuo Standard.
If you'll be camping on warmer summer nights or have a synthetic bag (that itself will mat beneath you to a degree and compress less than down under your shoulders, back, bottom, and legs/heels), then you likely won't notice the colder qualities of a lighter mat. If, however, you find your present sleeping bag is a bit on the cold side (especially if it is down), then a warmer pad will also give you an effectively warmer bag, 'cos you'll be losing less heat through your entire backside to the ground.
Others might well disagree, but as a general rule of thumb, I find I can better get a good, warm night's sleep using a marginal bag with a good pad rather than a fantastic bag and a marginal pad. On a poorly-insulated pad, I simply lose more heat through conduction than I can make up for with convective conservation. And yes,when it is really cold, I use all the tricks to keep as warm as possible with minimal weight -- side-sleeping in a fetal position with hands tucked under armpits, over groin, or between my thighs, the hood closed tight to just a mouth-hole, with a silk liner, wearing adequate clothing (including double socks, balaclava) in the bag, and careful choice of ground cover and overhanging vegetation and general location when possible (not right by a river or on an upslope) and being mindful of tent ventilation. All those things make a real difference to nighttime temperature conservation no matter what pad is used, but with a warmer pad, I usually can just...sleep, with few if any tricks needed.
That said, I'd prefer the Eped down 7 'cos the down in the chambers provides more isolation than a pure air mattress.
There is an alternative, which I have yet to try myself -- the body-mapped air mattress that goes
inside your bag. The Klymit X-Frame is the most common of this type. It works better if your size matches the pad's, but the idea is it allows the sleeping bag's insulation to swell up through the open parts of the air mattress and so provide more isolation that a conventional air-filled mat. I can't think of a pad that better hits the small/light combo, but (again) its success depends on being about the same size as the pad so your bigger-flatter parts hit the pad; if its a miss, it won't be as warm or comfortable.
The "con" to all the X-Frame "pros" is the areas that need the most support are still supported on air and still squash the sleeping bag in those same places, so except for being lighter and smaller, the pad performs about the same as an all-air pad.
Klymit's own website is here:
http://klymit.com/Here's some links to the several models they offer, with reviews: http://www.rei.com/search?query=klymit
*Earlier, I mentioned personal experience. Some people sleep cold and need a sleeping bag rated 10-20°F colder than people sleeping next to them. Other people are volcanoes, and only use their bags as loose duvets on the coldest of nights. I sleep "normal" at mid-temperature range until.... "Until" means when I am dehydrated, when there is an 80°F difference between daytime highs and nighttime lows and I feel the contrast, or when I am hungry, overworked, and tired from slogging along through playa for 17 hours at a stretch. Then, I don't sleep as warmly as usual, and really appreciate a warm pad, weight be hanged. I call the 1kg weight of my pad a "luxury necessity", as it allows the unbroken sleep I need to keep going day after day. I'll scrimp in weight elsewhere, but oh, that pad; gotta have it.
Hope this helps.
All the best,
Dan. (...whose nightly bed at home is a Nemo Tuo Luxury pad on plywood in a bedframe beneath the usual sheets, blankets, and bedcovers)
