How to Cut Styrofoam

Cutting Styrofoam Manually

Use a blade for straight cuts. Bladed implements like knives, box cutters, precision blades (like X-acto knives) or hacksaws are great for cutting through styrofoam, especially if you don’t need to make any curved cuts. For a smoother cut, run the blade along an old candle before cutting your styrofoam. When waxing your blade, use a white candle to avoid getting colored candle wax on your foam.

Use dental floss for cutting through styrofoam sheets. Dental floss is great for cutting straight lines through sheets of styrofoam. Lay the styrofoam down with the floss underneath it. Line the floss up along the line you want to cut through the styrofoam, then place one hand on the styrofoam sheet to. To slice the styrofoam, pull the end of the floss furthest from you towards you.

Use cookie cutters to make unique shapes. If you have a relatively thin piece of styrofoam (no more than two inches or five centimeters thick), you could use a cookie cutter to cut through styrofoam. Just press the thin edge of the cookie cutter into the styrofoam until it punches through to the other side. The styrofoam piece that results will be in the shape of the cookie cutter.

Try cutting it underwater. If you don't want to make a mess, you could try cutting styrofoam underwater; that is, submerging a piece of it in a tub or bucket filled with water, and cutting the styrofoam underwater with a knife. This prevents the small crumbs that come off from flying all over the place, enabling you to make a faster, and hence smoother, cut. Remember to strain the water before pouring it out. The cut styrofoam block can easily be patted dry afterwards, as styrofoam does not absorb water.

Cutting Styrofoam with Electric Tools

Use an electric knife to cut thicker pieces of styrofoam. If you’re cutting through several pieces of styrofoam at once, or through a single piece that is several inches (several centimeters) thick, an electric knife is your best bet. They’re best for making straight cuts, but they could also help you make a gently curving cut.

Use a foam cutting saw to cut through larger pieces. Foam cutting saws are the best option for cutting through large bricks of styrofoam like those used to package televisions and other large appliances. However, they’re also the most expensive option, and tend to range from about $150 to $400 USD. Generally, you can just turn the saw on and press the piece of styrofoam you wish to cut into the blade, keeping your hands clear of it. Consult manufacturer directions for the particular type of saw you’re using. When using a power saw to cut styrofoam, wear a dust mask and safety goggles. Power saws can create a "foam dust" that is similar to sawdust, but can irritate the lungs if inhaled.

Utilize a hot wire cutter for smooth cuts. Hot wire cutters melt through the foam with a heated wire, creating a smooth edge. They are especially effective for creating rounded edges or shapes out of styrofoam. Apply slow, consistent pressure with the hot wire cutter along the desired cutting line. Moving too fast through the foam will cause the wire to snap. Use extreme caution when operating a hot wire cutter because the wires are extremely hot and can cause severe burns. Hot wire cutters are great because they leave behind the fewest styrofoam crumbs and produce the smoothest cuts.

Making Various Cuts

Follow the directions for the craft you’re making. Sometimes you might make curved cuts first when cutting styrofoam, while other times you might make straight cuts. Either is acceptable as long as you’re following the directions for your project. If you’re engaging in a project of your own design and not working with directions, you can make either curved or straight cuts first. Remember, it’s your project, so there are no rules!

Use long, sawing motions when cutting with a blade. Keep steady, even pressure on the knife throughout the cutting process to reduce the chances of breaking or crushing the foam. Long, sawing motions will also minimize the amount of foam crumbs you produce.

Cut out indentations from the center of the styrofoam. If you want to cut a depression in styrofoam, start in the center. Draw a line around the area you want to remove, then select a tool that will allow you to remove it while achieving a depth and a degree of curvature that pleases you. A depression with vertical sides is best removed using a knife. Just select an appropriately long knife, then cut along the line you’ve marked. In some cases, indentations are best achieved using a rounded sanding tool rather than a knife.

Cut channels in the styrofoam using a bladed tool. A long, serrated knife or an electric knife is probably best for cutting channels through your styrofoam. Mark the length and depth of the channel on your styrofoam, then punch your blade through the styrofoam to the depth you marked. When the piece is loose, remove it. You can use this technique to cut channels that run through a piece of styrofoam or along the surface of a piece of styrofoam.

Divide round styrofoam balls by cutting them down the middle. You can cut a round styrofoam ball in half by tracing a line along its equator with a sharp pencil. Many styrofoam balls already have this line marked by the manufacturer. Use a sharp blade, a hot wire cutter, or an electric knife to bisect the ball.