How to Cut Fiberglass Insulation

Cutting a batt or sheet of fiberglass insulation can be messy and frustrating. The fiberglass is fuzzy and difficult to cut straight. Fortunately, a few simple steps can make the project much easier. Always protect yourself from inhaling shards of fiberglass or from coming into skin contact with the fibers by wearing a dust mask, eye protection, gloves and a long-sleeved shirt and long pants so there's no uncovered skin and no way for the fiberglass to get into your eyes or throat.

  1. Lay the batt of fiberglass insulation to be cut out on the plywood with the foil or kraft-paper backing facing up.

  2. Lay the 2-by-4 inch board along the line you desire to cut into the fiberglass. The board should be long enough that it sticks out 6 inches beyond the edges of the fiberglass batt on each side or at least 12 inches longer than the line you intend to cut.

  3. Weight down the board by kneeling on one end of it, then pressing down on the other end with one hand. This compresses the fiberglass and makes it much easier to cut.

  4. Use the utility knife, in your free hand, to cut through the fiberglass along the edge of the board as you continue to compress the fiberglass. You should be able to cut through it in just one stroke.


  • Be careful not to cut your knee or fingers as you cut through the fiberglass.