I have (2) of these. The Exped's have an R-value of 4.9. So they are warm. Equal in warmth to the Stephenson Dam even though they're a little less in thickness. More down I would guess, since they weigh about the same but are narrower. But, I've had the slow air leak problem with them that other people have reported as well. This is where at about 3 in the morning you are on a flat pad. Finding said leak is a major pain. Best way I've found is soapy water, like looking for a gas leak.
I sent the original (2) I bought back and received a replaces free of charge from Exped. These current ones are the replacements. I'm not sure if I damaged them or if they came with the leaks. They always seemed to leak a little. But, I was never sure if it was the temps dropping or a leak causing the minor deflation. But, it has slowly gotten worse and worse.
I've repaired the leaks I could identify, but I just don't trust them anymore. 3 am is a bad time to get up and mess around with a pump that was your pillow.
I'm not inclined to send these back although I take excellent care of my gear and don't really feel I am at fault.
My advice, if you get one of these is to test it really well before you take it on the trail. Inflate it and sleep on it all night, preferably outside, where the temps will drop and it will deflate some from that as well. Determine for yourself if the pad is leaking from the git go. So you can return it, confident that it came to you defective.
These are really slow leaks that don't even show up under water, unless you apply quite a bit of pressure. But, they do show up over night.
Other than this problem the Expeds have been great. Comfortable, warm, compress down well.
So far the Stephenson has been fine. No leaks, no problems. The guy who makes them was friendly and tried to talk me out of my custom size. He's not an ultra light fan. But I persisted and he sent me the custom one.
I found the website offputting at first. Not because of the nudity. I didn't care one way or the other about that, but because the info was so scattered. But, I heard good things about the products and found I wanted something custom, so it was the only game in town, as they say.
Looks like he measured and cut it himself. You can see the measuring marks on it still. Fine by me. I'm into the function not the looks of the thing. definately not mass produced.
I've only used it a handful of times, so we'll see how it holds up. I'm impressed so far. And looking forward to having a floaty for the mountain lakes this summer.