The Best Way to Cut Styrofoam Insulation


Styrofoam insulation is an accumulation of small white foam beads pressed into rectangular shapes. The foam sheets are used for insulating spaces. Typical sheets for insulation are 4 feet by 8 feet. The Styrofoam can also be shaped into large blocks and used as flotation devices for boat docks and marinas. Various-size sheets or blocks require different methods of cutting. Cutting tools can vary from a razor knife, a handsaw or an electrically powered hot wire. The type of tool you use depends on how much money you want to spend.

Razor Knife Cutting

  • Thin sheets of Styrofoam, from ½-inch to 1-inch thick, can be cut using a razor knife. Measure the sheet with a tape measure. Mark the sheet: Place a notch at the appropriate place. Lay a straightedge along the marks. Pull the razor knife toward you in one smooth motion. You may have to run the knife several times over the cut to penetrate material thicker than ½ inch. You could use various straightedges, from carpenters' squares to drywall T squares, or even a long two-by-four board. Use a chalkbox for cuts longer than the straight edge. Notch the sheet of Styrofoam, and hold the chalked string in one of the notches. Pull the string taut to the other mark. Pop the string to release the chalk mark onto the foam. Cut the sheet to the identified line.

Handsaw Method

  • A wood-cutting handsaw with a fine-tooth blade can be used for thicker material. Lay the foam sheet on a pair of sawhorses to support the sheet off the ground. You will need clearance for the blade to cut through the Styrofoam. Mark the sheet or block of foam, using the chalk box as described above. The handsaw will be a little messy, as some small beads will break from the formed sheet or block. The saw will not be as neat as a hot wire, but the cut will be accurate.

Hot Wire Cutting

  • A hot-wire cutter consists of a single Nichrome wire suspended between a tensioned bow. Nichrome is a brand name for a nickel-chromium resistance wire, a nonmagnetic alloy of nickel and chromium.The wire is electrically insulated from the bow. An electrical current, typically DC power, passes through the wire. The electrical-resistance characteristics of the wire create heat. The hot wire melts the foam as it passes through the material. A hot-wire cutter is made to any size. The bow is constructed from a wood frame or bent from electrical mechanical tubing, also called conduit. Large hot-wire cutters are held between two people to perform accurate cuts. The cut line is again made from the chalk-box method. The hot wire is slower than cutting the Styrofoam with a handsaw, but the beads of foam melt back into place by the wire's action. Power sources for the hot-wire unit range from a simple 12-volt car battery to a sophisticated power supply. The power supply plugs into any home outlet, and the output power is adjustable to dial in a specific temperature for the wire cutter.

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