Are we talking about tin foil, or aluminum foil? I wrap my lids in aluminum foil on my aero system. The reflectivity I am not sure about, it seems shiny enough. I use it for its heat cooling capability, as well as blocking the spray from the slit in the lid (aluminum is not very corrosive). If you crumple it a bit, it has a lot of surface area which cools the whole area down and keeps the plant cooler (acts as a heat sink).