I picked up a roomfull of these foam flooring tiles (sold by Costco) for another project,
and am planning to use them on the ceiling. It fits my color and theme I think, but have not got to that point yet. I am not sure if there is any downside to them..I know this lowers the perceived height, but I have high ceiling. It cuts down on noise..but any issues? Not really seen it done! Must be a reason..