It is white and is very light, but it is hard rather than soft. Perlite is a natural, though heated, material. Styrofoam is completely man-made, expanded polystyrene, a plastic. Styrofoam will quickly make its way to the surface if used in potting soil (its 98% air), and though perlite can do the same, it doesn't do it rapidly, particularly if it is wetted before being incorporated into the soil. Some commercial growers (and I guess we hobbyists as well) might use Styrofoam in their orchid media, and the large, fir, pine, or cypress chunks keep the Styrofoam in place.
