I bought the foam board, 20″ x 30″ x 1/4″ thick from Dollar Tree. Same quality as the pricier 1/4″ board found at the craft stores. It comes in black and white. I chose white. I use the foam boards as the background for my photos. To cut, I use a straight edge with those little sticky pads on the underside which keep the straight edge from sliding on the material to be cut. I use a fresh blade on my Dollar Tree X-acto blade. Save your larger foam scraps to make the sandwich board!
This board is not the same as the foam board I have seen for the Science Lab! That foam is 1/2″ thick. I think that would require a much better blade than I use. And the foam is much more expensive.