Tip for Cutting Fiberglass Insulation Easily

To cut thick batts or rolls of fiberglass insulation easily, use an extendable utility knife that has snap-off blades. Extend the blade all the way out to provide a long, sharp edge that perfect for cutting through thick insulation.

Use a board to compact the insulation and provide a straight edge for cutting. Watch this video to find out more.

Further Information

Joe Truini: One of the best ways to save energy around your house is install your own insulation. It’s a pretty easy job, too, although it does require a lot of cutting.

Typically, if they can be cuts like every three or four feet, or six or eight feet, depending on where you’re installing insulation. So, the best thing is to set up outside if you can, so you keep the dust out of the house. And to use… First you put a board down that you can cut against, and you have a straightedge that you can cut along.

Now, even with insulation—this is only R13, but it’s about four inches thick. If you use a standard utility knife, you can see the challenge, the blade’s only about an inch long. So what I prefer to use is a utility knife that has a snap off blade.

Now, the way these are designed to be used is, you extend the blade, when it becomes dull, you snap it off, and you extend another blade. But you can also extend it three or four inches. What you end up with is this beautiful insulation cutting weapon that will slice through the thickest insulation.

So, just roll it out, get the length you need. And then, what I like to do is kneel on the board to compress it. Then with the long blade, you can very easily slice right through it.

There you go, through the insulation and paper. Now, if I can just get someone to help install it.


  1. Great video yeah I started out with using a dull knife slicing through the paper side and made a mess halfway through my cut I kept kneeling on my board to get better compression but still had to make several passes with a utility knife good tip thank you

  2. I know it sounds weird, but I found an inexpensive, long serrated bread knife worked wonders. Especially for the Roxul (mineral) type of insulation.

  3. I took a couple of 2×6 boards and an old door hinge to fasten the ends together, making certain to off-set them by about 1.5 inches. so they act like an insulation compression device.
    Then open the hinge, slip the insulation between the hinged boards and place your knee on the free end of the top board to pinch and compress the insulation between the boards.

    Now, it is easy easy to cut with a utility knife.


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