I don't have any resources other than first hand experience, but there were 3 of us using these last weekend and all of us could tell a difference. I was sleeping with my head under my tq/sleeping bag and when I woke up and poked my head from under the bag of course there was a huge difference. When I would pull the sock down I could feel another huge difference. I didn't have a thermometer and could not tell you exactly what the variation was, but I feel it definitely meets Dutch's claim of 10-15° and may even exceed it. Lows for the nights were 27°,32°,36° I believe. It fits in the stuff sack that came with my hammock, and serves double duty as an under quilt protector. YMMV, but I hope that helps.
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