I'm not afraid to say it. I got suckered.
I bought the $65 Thermolite Reactor Extreme from Sea to Summit. Through extensive testing, I found that the material did little to nothing to increase warmth, a far cry from the advertised 25º.
First off I read "Can be used as a summer sleeping bag!" as fact, and brought it with me on a 30-day, 1500-mile bike tour across the northeast that included summits of Mt. Caddillac, Mt. Greylock, and Mt. Hurricane. We slept on Hurricane and it got to 40º; luckily, after 3 days of touring I established that the thermolite liner did next to nothing on it's own, and I grabbed a $30 fleece bag (Alps Mountaineering RAZOR). Had i just had the liner on it's own, I may still be shivering to this day.
I can detect no difference sleeping with and without the liner using the fleece bag.
I can detect no difference sleeping with and without the liner using a 20º synthetic baffled bag.
I can also attest that it blocks no wind whatsoever- the nature of the hollow-core fibers don't block a damn thing. With a 20º bag, this product is advertised to make my sleeping bag into a -5º system, and I'm still a bit chilly at 30º. I would argue that at -5º with no clothing, a 20º bag, and the liner, I would probably die.
If it is providing warmth, it's less than 10º as far as I can tell. I am disappointed, but hey- live and learn. It doesn't end up in my pack anymore- my Merino Wool baselayer does much more.