Ceiling medallions and domes are manufactured with a dense architectural polyurethane compound (not Styrofoam) that allows it to be semi-flexible and 100% waterproof. This material is delivered pre-primed for paint. It is installed with architectural adhesive and/or finish nails. It can also be finished with caulk, spackle and your choice of paint, just like wood or MDF. A major advantage of polyurethane is that it will not expand, constrict or warp over time with changes in temperature or humidity. It's safe to install in rooms with the presence of moisture like bathrooms and kitchens. This product will not encourage the growth of mold or mildew, and it will never rot.