Consider the following:
There are two properties on which radiant barriers work: Reflectivity and Emissivity. If you consider aluminum remember it is reflective on the hot side, reflecting some of the heat back from where it came. Second, and most importantly, aluminum has a low emissivity of between 0.03 and 0.05. This means that only 3% to 5% of the heat is emitted to the air on the cold side. In order to benefit from both of these properties, the radiant barrier must be double sided (aluminum on both sides) and installed so that there is an air space or low density material (like insulation) on both sides.
Technical Specifications
