And you would know that from your first hand experience with it. Maybe you didn't read my post. I ran a little mock setup last night, for a total of five hours i ran the unregulated flexwatt with a big thick book right on top of it. Trying to achieve the hottest temps i could. I measured the heat with a temp gun, it ran a consistent 188 degrees with the book on it. I bet if I do the same test on a tub it will melt. I have another test i an gonna run but if it passes like it did last night I am gonna use it.