Only my experiences and not to counter anyone's thoughts...
I've owned both of these pads. I owned the Exped Downmat 9 first (bought in 2009) and it did indeed have a baffle failure after about 4 or 5 years. I contacted Exped USA directly and they replaced it with zero hassle. I didn't have to return the defective mat; they just had me send a couple images via email and had a new one on the way to me in 24 hours. I was told there were improvements made in the interior construction, but cannot verify that. I will tell you I've had no issues with my current Downmat and I trust it completely every year for 2 weeks in Alaska. It is BY FAR the warmest, quietest and most comfortable mat I've ever slept on period. I trust it 100%.
I bought the XTherm in 2015 for a solo caribou hunt in Alaska, as I didn't need the warmth of the Downmat. I thought the XTherm was generally comfortable though not as nice as my Exped. I found the surface of the mat to be a little slicker and my bag wanted to slide more. The 100% most bothersome thing about the XTherm for me was the noise factor. I could not move, adjust, turn or do anything on it without causing it to make a lot of crinkling/crackling noises in the night. I don't ask for a lot, but my bed needs to be quiet. I know this same issue (for me) is a non-issue for others, so it's a matter of knowing what you'll tolerate. Despite the negatives I thought the XTherm was an overall great pad.
In the end, I knew the XTherm was always going to be the pad I'd have to argue with myself to take. The Downmat would always win for quiet, warmth and comfort. I sold the XTherm after one season and have not wished for it since. If I had no experience with either pad...I would purchase BOTH and do a side-by-side eval in the home. Keep the best of the two and return the other.
