We had the radiant barrier put in almost 6 years ago. There was nice 35% reduction in the A/C electric usage (I have been tracking kwh for years now and calculated two years pre versus two years post installation). But I know the old A/C units were inefficient. We just had new A/C systems installed last spring and the effect of the radiant barrier is amazing. I can't wait to see longer term results but a calculation of the savings from just this past year is over 20! I love it!