^ He was probably worried about delamination; I thought about it too but I haven't heard of it happening yet.
Anyway, I tried this out while camping this past weekend. Brought a 24" x 10' roll and a pair of scissors with me to cut out during my down time. I know this will serve 2 main functions:
1) Keep heat out, and cold in
2) Keep cold out, and heat in
This weekend was a test for #2, as it was pretty chilly overnight @ 7,900 feet. I couldn't help but notice the difference in temperature when touching the glass, and then touching the Reflectix that was over the glass. Night and day. The glass felt very cold; the Reflectix didn't have a hint of chill. I covered 10' worth of glass, and compared to the previous night, there was a noticeable difference - the "chill" in the air inside the truck that came through the glass was pretty much gone.
Driving home took us through the desert, reaching 98 degrees...so I got to test #1 as well. Same story here - the back section was dark and cool; the front of the cab was bright and hot. It makes a hell of a difference. I was able to stay comfortable with my A/C on the low setting (fan speed 1), when I would typically have it on fan speed 3 out of 4 in 98 degree weather. The A/C didn't have to work as hard.
I usually sleep in the back of my truck, and the Reflectix sheets I cut out are now primary pieces of travel gear.