Styrofoam, which is also known as polystyrene, is a hard foam material often used in building props and models. The foam is used as a "core," or inside piece, for a fibreglass or other plastic coating. In order to use styrofoam as an effective core piece, you must first form a block or sheet of the material into the shape you need for your project. This may require cutting and/or bending before the styrofoam is properly shaped for your purposes.
Lay the paper pattern for the object you want to make over a styrofoam sheet or block. This should be a simple drawing of the overall shape you need the styrofoam to have. You can tape the paper pattern in place, if necessary.
Apply a small amount of wax to a craft knife so that the knife will cut smoothly. Cut the styrofoam along your paper pattern lines until you have a rough overall shape.
Remove the paper pattern from your styrofoam piece. Refine the shape by carving around your cut edges again. If you would like a smoother line, you can use an electric, hot-wire styrofoam cutter.
Add the texture you would like your styrofoam piece to have. If you are making a prop, you may be looking for a rough or rock-like texture. Flake pieces of styrofoam off the overall piece using tools like a wire brush, an ice scraper and a cheese grater.
Bend your styrofoam piece if you require a curved shape for your project. Take a few wooden dowels or pieces of wood in the size curve you need, and fit the styrofoam piece around them. Clamp the dowels together, sandwiching the styrofoam between them.
Fill a plastic tub with water that is heated to 90 degrees Celsius. Immerse the clamped styrofoam in the water. Do not touch the hot water with your hands.
Remove the styrofoam from the water once it has cooled enough to touch. Remove the wooden dowels. Your styrofoam piece will have formed to the shape of the dowels.