Struggling to slice through thick fiberglass insulation? A standard utility knife won’t cut it—literally. The trick is to use an extendable utility knife with snap-off blades. Here’s how to make clean, precise cuts every time:
- Extend the Blade: Snap-off utility knives can extend three to four inches, giving you a long, razor-sharp edge perfect for thick insulation.
- Use a Board as a Cutting Surface: Lay a scrap board underneath to create a solid base and a straight cutting guide.
- Compress Before Cutting: Kneel on the insulation or press it down with the board to make it thinner and easier to slice.
- Slice in One Smooth Motion: With the extended blade, glide through the insulation and paper backing in a single stroke.
Cutting insulation can be messy, so if possible, set up your work area outdoors to keep fiberglass dust out of the house.
Want to see this method in action? Watch the video above!
Frequently Asked Questions
What is the best knife to use for cutting fiberglass insulation?
A standard utility knife works for thinner insulation, but for thick batts or rolls, an extendable utility knife with snap-off blades is the best choice. Extending the blade three to four inches allows for cleaner, more efficient cuts through both the fiberglass and the paper backing.
How can I reduce fiberglass dust while cutting insulation?
Cut insulation outdoors if possible to keep fiberglass dust out of your home. You can also lightly mist the insulation with water to minimize airborne particles. Wearing a dust mask, safety glasses, and gloves will help protect you from irritation.
Should I cut insulation to fit snugly or leave extra space?
Always cut insulation about ½ inch wider than the space it’s going into. This ensures a snug fit and prevents air gaps, which can reduce insulation effectiveness. However, don’t overstuff—compressing insulation too much can reduce its R-value.
What’s the safest way to handle fiberglass insulation?
Wear long sleeves, gloves, safety glasses, and a dust mask to prevent skin and respiratory irritation. Avoid rubbing exposed skin, and if fiberglass fibers get on you, rinse with cold water before washing with soap to avoid embedding fibers into your pores.
Can I use scissors instead of a knife to cut insulation?
Heavy-duty scissors or insulation shears can work for thinner insulation but may struggle with thicker batts. A sharp utility knife with an extended blade is the best tool for clean, straight cuts, especially when combined with a cutting board for support.
