If you are making a foam sculpture, soft set of dice or any type of project that involves making a cube of foam, you can cut the cube yourself. Foam cubes in the size you want may be difficult to find, so making them yourself, from a larger piece of foam, may be the most feasible option. Use the proper tools to cut the cube, depending on the type of foam you use.
Draw a square onto one side of the foam, the same size that you want each side of the cube to be. Use the ruler to measure and draw the straight lines.
Cut along the drawn lines all the way through the foam. If you are using foam rubber, such as that from a sofa cushion, or polystyrene use a serrated knife to cut it. Use a craft knife or utility knife to cut craft foam.
Turn the cut shape on its side to reveal a side that is not the right size. Draw another square, the same size as the first square, but draw it so one side of the square shares an edge with the one you already cut.
Cut along the drawn lines, all the way through the foam again. Your cube should be beginning to take shape now, save for one side.
Flip the foam one last time to reveal one side of the length of the cube that is longer than the others. Draw a final square, sharing the edges with the previously cut edges from the other two cuts.
Cut along the lines of the final square, all the way through the foam. The foam cube should be completely squared on all sides.