Oh gee I can't stay out anymore. Time to give my two cents, I'm feeling analytical tonight.

The way I "see" it --lol--we're comparing apples to oranges, for most practical purposes. Khronik stated that aluminum in it's nearly pure form, has a high reflectivity. I can buy that. Polish it, the reflectivity goes up. I can buy that too. However, when we say "foil" it all goes to h#ll in a hand basket, like Goldenass briefly touched on.

Why? Because foil is an alloy, for one. But just as important, is the fact that the surface texture of foil compared to that of mylar, is VERY different. Put them under a microscope and just analyze it visually. Thirty power should do it.

Personally, I think the reflectivity of a given material is mostly in it's surface texture. A point can be made regarding how far into a material, that the light beam travels, before being reflected. A mirror appears to be a good reflector to the naked eye. But we all know better. Why, because the light beam has to actually travel through the glass, before it hits the actual "reflector" on the back side of that glass. Then, it has to travel back through the same thickness of glass again, before it reaches a plant to be absorbed. Common knowledge for the posters above me, sure, but maybe someone else can use the info.

As far as I know, IR has done the true test with a verifiable light meter, in the proper environment no less. So, I guess the proof is in the pudding.
ProGroWannabe Reviewed by ProGroWannabe on . Mylar vs. foil For a long time I assumed everyone knew what they were talking about when they said not to use aluminum foil, and to use mylar. Apparently foil can create hot spots. But here's the thing, so can mylar. In fact, it's often used precisely because of its ability to reflect heat! Anyway, I've heard all sorts of misinformation, like that aluminum foil is only 40% reflective whereas mylar is 98% reflective. So I looked up some data in my thermodynamics textbook from college. Actually, Rating: 5