Tinfoil might be ok with cfl's, but the fact that cfl's are only effective up to a couple inches, the light reflecting from the tin foil/white walls won't have much effect on your plants. I have never seen anyone recommend tinfoil just because of all the problems (wrinkling reflects light where you don't need it, hot spots), especially since he's got 2 HID's, and not cfl's. Only way to know for sure is to use it, but since people have had more problems with tinfoil than success, I sure wouldn't use it nor recommend it in this case, or any for that matter. Just my :twocents: