Today was the first day since I installed radiant heat barrier foil that was hot enough (97degrees) to collect some good data. I went around the house with a digital thermometer and collected some temp. readings. As you can see from the colorful diagram I made the foil works. There is an 11 degree temperature diiferential on either side of the foil. I got the foil from Atticfoil.com for around $135/thousand sq ft. This is about half the price of what Home Depot and Lowes charge for this. By my calculations it will pay for itself by the end of summer.