Ive been looking into it, seeings as i'm going to have to do a lot of work in the attic, i would rather get all of the hot stuff done at once. I will be spraying in f-glass / cellulose insulation which i have calculated out to 10$ per bin (40 sq ft), and i will need approximately 40 bins , so a 400 dollar investment with free blower rental should get my house to a high R rating, to cope with these Houston summers. but first i would like to address the radiant barrier potential. I'm basing this off of this type of foil insulation. which a contractor pack of (50) 24"x48" sheets is 200$ at home depot. assuming i would need at LEAST 2 packs (if not 3) to do my attic, im looking atleast a 400$ investment. for what i have heard is a r-value of MAYBE 1. I understand there are several types of radiant barriers, but for this discussion, lets assume its the foil type. Now I can understand the theory, that the aluminum "foil" backed insulation reflects alot of the heat rays back out. but when its put installed beneath the plywood, and overstacked shingles, what rays are really penetrating that far in. mainly for the cost of the insulation, if you were to have houses, with identical R38 insulation sprayed in in the attic, and only one house had the radiant barrier installed. identical houses, in identical correlation to the sun, would there be any notable difference? it seems like its extremely expensive (in comparisson) for a very little increase in cooling. anyone have any input? It almost seems like snake oil to me. it wont serve any purpose other than piece of mind.