Q&A for How to Cut Styrofoam

Think of the wax as a lubricant, it allows the knife to go through the product faster.

Not a good idea. Even a fine grit will tear the foam: think rough sand against a very smooth surface. Instead, use a spare piece of foam get rid of the burs. Just rub the foam piece gently against the cut edge.

Yes, and the ones that work best are the ones with a serrated blade.

Cut it into a half-sphere first using a hot wire cutter, then use a knife to scoop out the insides of the bowl.

Very carefully! Use a variety of tools -- knives, floss, and wire cutters -- to achieve the desired affect.

It depends on what you want to create. If you require a full ball, then don't cut it. However, if you purchased a Styrofoam ball for a flat project, then yes, cut it in half before you start.

Mark the area with a marker, then use an X-acto knife to cut out the piece.

It is already transparent. Being a foam, each time the light passes through one of the thousands of layers it is made of, the light gets scattered a bit, so it looks like it is white. By the way, that's exactly the same reason why it is a good thermal insulator. You can verify that it is indeed transparent by melting it with few drops of acetone.

Measure the middle point of 11 1/2". Use a strong knitting needle or pin and push it through the center and almost into your work bench. Direct your cutting wire to 5.5 1/4" (the halfway mark of your circle diameter). Rotate the bigger piece while holding the knitting needle very stable. The outer edge will be trimmed away to your required size.

I mixed plaster of paris as per the mixing instructions on the package, then covered the Styrofoam rocks by spreading the the plaster of paris with my hands. It takes a few minutes to dry, or maybe an hour, depending on how thick you spread it on. Then you can add more layers if you wish.

Try using a jigsaw or reciprocal saw. I found they cut through sheets 40 mm thick like butter and leave an extremely smooth edge.