How Do You Cut Fiberglass?

Updated February 21, 2017

Fibreglass has many uses in and around a home, including fibreglass insulation, hard wall coverings and repair tape. When installing fibreglass insulation, cutting is necessary to fit the batting into a void space. Cutting fibreglass tape to size is essential to a finished wall repair. Fibreglass wall panels or bathtub surrounds require cutting to fit into the areas to be covered. The cutting method depends on the type of fibreglass material being used.

Stretch the fibreglass tape from the beginning point to the end point along the wall.

Press the tape in place with your fingers to secure it to the wall.

Slice through the tape at the end point with a sharp utility knife.

Lay the fibreglass insulation on a flat, stable cutting surface, with the foil or paper side facing up. Stable cutting surfaces include a sheet of plywood or drywall, or a workbench.

Draw a cutting guideline directly on the fibreglass batting.

Place a straight piece of wood, such as a 2-by-4-inch board, on the line. Kneel on the wood to squash down the insulation.

Cut along the edge of the wood with the utility knife. Press the knife into the line and through the insulation while dragging it along the guideline. You also can use large shears to cut along the guideline.

Measure your cutting lines on the back of the fibreglass panel. Mark the lines with a dark marking pen.

Place the fibreglass panel across two sawhorses. Secure the panel to the sawhorses with C-clamps.

Place masking tape over the cutting lines. Masking tape helps prevent the edges from cracking and splitting while cutting. Redraw the lines if they are hard to see through the tape.

Equip a circular saw with a high-tooth-count carbide saw blade to produce a smooth cut. Set the saw blade's depth 1/8-inch deeper than the thickness of the fibreglass panel.

Turn on the saw and cut slowly along the guidelines. Do not "push" the saw through the fibreglass material, because it can damage the panel.


Wear a protective jumpsuit, respirator mask, safety goggles and gloves when cutting fibreglass insulation. Wear safety glasses and a dust mask when cutting fibreglass panels.

Things You'll Need

  • Utility knife
  • Plywood, drywall or workbench
  • Wood scraps
  • Large shears (optional)
  • Marking pen
  • Sawhorses
  • C-clamps
  • Masking tape
  • Circular saw
  • High-tooth-count carbide saw blade
Cite this Article A tool to create a citation to reference this article Cite this Article

About the Author

Sal Marco began writing professionally in 2009. He has written many online home improvement articles based on his more than 20 years of experience in the home improvement and building industries. He has worked as both part of a team and as a site supervisor. Marco has a Bachelor of Science in management science from Kean University.