Reflective Aluminum Foil Insulations don't absorb heat, they block the flow of radiation.? Installing Reflective Aluminum Foil between the heat source (sun) and an existing insulation will improve the effectiveness of the R-Value rated insulation.?The reason is that only little part of the heat is now hitting the R-Value rated insulation and therefore, it will take longer for it to absorb 100% of its potential thereby holding the heat longer before passing out the back side into the room. Reflective Aluminum Foil reflects up to 97% radiant heat striking its surface.