One sheet of tinfoil is the same width as the sides and I stuck it on there with electrical tape so that it blends in with the black edges of the tank. I can't say that the tinfoil is the only thing that is keeping the ambient temps in the mid 80's range but when I didn't have the tinfoil it was in the low 70's. The temp could be a combo of the top being covered, the UTH heat radiating from the bottom and the regular temp in the room. All I know is it works well for me and like I said in the video he has had two good sheds so far. Also, as you can tell that tank is pretty big for that little snake and it doesn't bother him. Of course that could be just my snake and any other would be totally stressed out. I got the glass tank not knowing the benefits of a tub or anything about proper husbandry for BPs. I was totally ignorant and should have read up on it first but I learned and that solution works for me. I actually put the foil on there because I was using a heat lamp but when I switched to a UTH and the temps worked I left it on there.