Although RadiantGUARD radiant barriers BLOCK 95-97% of radiant heat, your utility bills savings will vary because some homes are more energy efficient than others and because of other forms of heat flow in a building structure that contribute to the total cooling (or heating) load.  Data varies by region.Direct quotes from a radiant barrier study performed by the Tennessee Valley Authority help to point out the heat transfer reductions you can expect although heating and cooling economic savings will vary based on other types of heat flow and local climatic variations:--All the radiant barrier configurations tested yielded sizable percent heat transfer reductions (ranging from 16 to 40 percent) and statistically significant reductions in summer attic heat transfer compared to the non-radiant barrier case.  Also, as the ambient temperature increased, the reductions also increased.--The radiant barrier configurations provides statistically significant winter attic heat transfer reductions in many, but not all, situations. The percent reductions during night hours and during below 35 degree F conditions, when heating loads are highest, are usually sizable (from 6 to 23 percent) and the differences between the radiant barrier configurations and the non-radiant barrier case are often statistically significant during these conditions.Note:  Note: The above study was conducted in Chattanooga, Tennessee and references radiant barrier performance tests when used in conjunction with R-11 and R-19 insulation however, R-30 is the least amount of insulation permissible under 2006 IECC.  R-11 and R-19 are not reasonable baselines in 2009.