Simple Solutions

Tip for Cutting Fiberglass Insulation Easily

By: Joe Truini

Using an extended blade utility knife to cut fiberglass insulation.

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

Video Transcript

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.


Please Leave a Comment

2 Comments on “Tip for Cutting Fiberglass Insulation Easily”

You can follow comments to this article by subscribing to the RSS news feed with your favorite feed reader.

  • Ben Says:
    March 26th, 2018 at 11:31 am

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

  • Robert Thomas Says:
    November 28th, 2017 at 11:05 pm

    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

We want to hear from you! In addition to posting comments on articles and videos, you can also send your comments and questions to us on our contact page or at (800) 946-4420. While we can't answer them all, we may use your question on our Today's Homeowner radio or TV show, or online at

 characters available

Tip for Cutting Fiberglass Insulation Easily