That's a great question! It really depends on what the tank is made of. My plastic tank and glass bowl only produce condensation on the inside of the lid, but some tanks may do it. I would recommend going to the dollar store and grabbing a few laminate place mats and put a towel down first, then the mats, then the aquarium. depending on the size of the tank, you could really put anything under it just in case as long as it fits.