How to Cut Foam Board Insulation

Foam board insulation is an inexpensive way to add a little extra R-value to your garage door, tool shed or other work spaces in your home or shop. However, it can be very messy and cumbersome to cut. Because foam board insulation is made simply out of expanded foam, using a hot cutting method is quick and easy.

Foam insulation installation

But if a hot cutting method isn't an option, the next best method is using a craft knife with an adjustable blade.

  1. Mark the foam board where cuts are needed.

  2. If using a soldering iron, wrap a 12-inch piece of wire around the end of the tool that heats up while the unit is cool, leaving four to six inches to use for cutting. Plug the unit in until it gets hot.

  3. While the wire is hot, allow the hot wire to melt through the insulation board.

  4. If using the craft knife, extend the blade longer than the thickness of the foam. Use a sawing motion to cut the board.

  5. Install the board in the area it was intended for.

  6. Warning

    Stear clear of the hot end of the soldering iron. Put the blade away when not using the knife.