I don't know whether it's a good a idea or not, but my original thinking that you'd have enough water mass to diffuse the heat sufficiently fast so that the coa

I don't know whether it's a good a idea or not, but my original thinking that you'd have enough water mass to diffuse the heat sufficiently fast so that the coating would not be be subject to very high temperatures at a given location. Obviously the heat would have to transfer to the exterior environment in some way (e.g. through the floor) so this wouldn't work with smartphones.