2 Mil Reflective Mylar 48 inches X 50 feet

This mylar is flexible yet thick enough not to crease easily. It suits my purposes well for good reflection. As for its precise reflectivity, I do not have a good setup yet to measure source incident light and compare that to reflected light. I could rather easily see a well lit scene through the film, so I almost posted a quick conclusion that the reflectivity must be lower than advertised, but then I thought it would be due diligence to take at least some measurement. I used a Gossen LunaPro meter to check direct incident sunlight on a clear day, and for those familiar with camera film, I got a reading of 1/125 sec at f/14 for ISO 100 film. Wrapping the film over the meter, I got a reading of 1/125 sec at f/2.2 for ISO 100 film. As an approximate calculation, this puts the direct light at about 25 times stronger than the light that passes through the film. If as much as 1/25 of the light passes through the film, then that would be about 4% loss there. Again, this was a fairly quick test, under no more control than having a clear sky and pointing the meter in about the same direction (toward the sun) without and then with a film covering. Still, since the human eye can see remarkably well in both bright light and near darkness, it seemed appropriate to see what a light meter might show.As I was unrolling some of the film to do this test, I could not help but notice the intense heat and painfully bright light reflected back at me. I can't speak to the exact wavelengths of light that are reflected or lost by either surface absorption or pass-through, but I was not at all upset with the reflective performance. My impressions are very positive; I am pleased with this purchase.

Granted, this isn't a scientific claim on my part, but this material passes enough visible and IR light to navigate a fluorescent-lighted indoor space when used as sunglasses, and my IR remotes still work when wrapped in the stuff (although not as good, as you would expect). I have no idea in what part of the spectrum they are talking about when making this claim of 98% reflectivity, but I find it hard to believe it's anything in the visible or near-IR range. It would be better described as reflective tinting. This alone is my reason for the 3/5 rating.Durability is fairly good based on initial handling anyway. One side is more reflective than the other, and that more reflective side is a fingerprint magnet. Wear gloves unless you want to have your pretty surface smudged in finger goo. The other side doesn't seem to pick up prints much.Cleaning is possible with mild-soapy water and a lint-free cloth, although I don't know what is officially recommended. That worked for me.Heat can be applied to shrink it a bit. Too much and it turns to a dull gray surface, but will stay reflective to a point.It probably is 2 mils - I smashed together 4 layers and it measured between 0.0070 and 0.0095" depending on where the measurement was taken, which confirms your guess that it's not 2 millimeters as the title suggests - 1 mil = 0.001 inch, NOT 1 millimeter.My plan is to use this in a outdoor application, so it remains to be seen whether it will hold up to the elements. As they did not make such a claim in this regard, it'll just be my loss if it fails.