Styrofoam ceiling panels are very popular because they are used in drop ceilings. They are not expensive to buy and they are very stylish. They are also easily cut to size to fit where they need to go. This makes them very easy to install. They can also be painted very easily.
They can be bought in many places. Most lumber companies or building supply stores will have them in stock. If they do not have them, they should be able to order them for you. There are usually a few styles to choose from in these. Thicknesses may also vary slightly. More info: styrofoam ceiling tiles