Heh, I like the look of foil better. Plus it's safe if it is in contact with a heat lamp, which saran wrap is not. But if it's a long term solution (in other words, a tank that the snake will live in long term as an adult, as opposed to a more temporary one that the snake will outgrow) I'd say it's worth making a cover out of plexi, glass, melamine, pvc, or some other solid material with air holes in it that you can cover and uncover as needed without having to mess with foil or plastic wrap all the time.