What you have in there is not true Mylar. The stuff you have is like a space blanket and the creases are bad. it is not very thick so you are not reflecting as much light as 3 layers of that stuff. 2 mil mylar is really good stuff. I recommend that you just sand down the interior of the box and paint it a commercial indoor ceiling white found at home depot. it will reflect most of the light like mylar but sill keep the temps down.