I used Gorilla Glue on mine, using the pink foam boards. It is nearly impossible to separate once glued. You'll break the styrofoam before breaking the bond. Two things to keep in mind when using Gorilla Glue. One, it takes about two hours to bond, and about 8 to cure. Also, it expands, so you'll need to weigh down or clamp your two pieces together. When carving, I found it easier to carve before gluing, because the glue bond is tougher to cut than the foam, but not impossible.