The rough porous surface of Styrofoam can make it a challenge to paint. This is a guide about how to paint Styrofoam. read more
So I'd suggest that you don't use spray paint. If you have to, coat the surface of the foam with a crsfts glue and then spray paint. You can also use acrylic paint although this will take significant amount of effort and time. Since it is porous, you might have to give multiple coats for the painted surface to look even and nicely done. read more
If you need to use a paint that's not Styrofoam friendly, you must first cover/seal the Styrofoam. There are many products used for this task, plaster of Paris being the most popular. However you can also use products like Mod Pod or surface textures. The best product to use is "Foam Finish". read more
Even if a paint is compatible with Styrofoam, one should keep in mind that multiple layers of paint will be needed to evenly coat the nooks and crannies in the material. Alternatively, another product can be used to coat the Styrofoam first so that otherwise unsafe paints can be applied. read more