EPS is expanded polystyrene, while XPS is extruded. The EPS will absorb more water than the XPS, and is more likely to crumble around the edges. In my opinion, the biggest thing I don't like about EPS is that if you have to cut it, you get those tiny beads everywhere. You can google the differences and go with what you feel will be best. I don't see a problem using the EPS.