Design or acquire a pattern for your sculpture. The pattern can be printed on any kind of flexible material such as paper or fabric, as long as it can be transferred easily to the foam.
Transfer the pattern to the foam. If necessary, stack the foam pieces together in the way they will fit for the finished piece and glue them in place. If the item is small enough or the design lends itself to doing so, pin the pattern onto the foam for easy tracing. Alternatively, you can draw the pattern by hand onto the foam without a pattern. Another method is to project the pattern onto the foam. Use a permanent marker to trace the pattern, or use the handle of a knife to press an outline into the foam. Remove the pattern once you are finished tracing it.
Put on your safety gear. Cutting foam generates very small foam particles that become airborne and can cause respiratory problems.
Carve out the pattern on the foam using foam sculpting tools.
Remove larger sections first then remove smaller and smaller pieces as you get closer to the pattern lines. You will want to end up shaving small bits of foam away as you approach the pattern lines.
Add finishing touches by sanding the sculpture to give it a smooth surface. Detail the piece with the smallest foam sculpting tools as desired.
Assemble any separate foam components and glue them together if required. Use wooden skewers to hold the pieces in place until the glue dries.
Coat the finished sculpture with plastic coating.