How to Cut Foam Insulation Sheets

Cutting Straight Lines

• 1

  Measure the area that the foam insulation sheet will cover.

• 2

  Draw lines with a permanent marker to mark cutting lines on the insulation sheets. Use a straightedge when drawing long, straight lines to keep the cutting line from becoming crooked.

• 3

  Place a sheet of plywood on top of two sawhorses or on flat and level ground. Lay the foam insulation sheet on the plywood.

• 4

  Plunge a utility knife into the cutting line. Pull the utility knife along the cutting line to cut the foam insulation. Hold a metal straightedge up to the line firmly with your other hand to guide straight, long cuts.

• 5

  Continue to pull the blade along the cutting line until you cut along the entire guideline. If the thickness of the foam insulation sheet exceeds the depth of the blade, plunge the utility knife's blade into the cut line a second time and cut along the line until you cut completely through the foam sheet. Repeat the cutting process for each sheet of foam insulation.

Cutting Holes

• 6

  Draw the circle on the foam insulation sheet with a permanent marker.

• 7

  Equip a power drill with a hole saw.

• 8

  Lay the foam insulation sheet on top of a sheet of plywood. If the insulation is already on the wall, cut the hole while the insulation remains on the wall.

• 9

  Line the hole saw up to the circle guideline. Turn the drill on to cut the hole through the sheet. If you are cutting a hole in existing foam insulation, the hole saw may kick back when you hit the material under the insulation.