Cutting fiberglass isn't difficult, it just takes a little longer in order to ensure safety and precision. Batts of fiberglass are thick and fuzzy and can cause skin irritation if your skin isn't protected. Fiberglass panels are cured hard. These panels require diamond blades and power saws. Wear appropriate clothing and safety gear, follow a few simple steps, and you too can cut fiberglass neat and clean every time.
Lay the fiberglass insulation on top of a piece of scrap plywood with its foil or kraft-paper vapor barrier facing up. The plywood underneath the fiberglass should be as large, or larger, than the piece you are cutting.
Cut a 2 by 4 piece of lumber at least 12 inches longer than the width of the fiberglass insulation. Place the 2 by 4 across the batt of fiberglass on the line you will be cutting. In other words, the side of the length of the 2 by 4 will be your cut line.
Compress the fiberglass insulation by kneeling on one end of the 2 by 4 and pressing down on the other end with your hand. Using a sharp utility knife, cut through the fiberglass in a single slash. Scissors of course are an option, but not usually recommended.
Use fiberglass power trimmers when cutting fiberglass panels. The 3-inch fiberglass trimmer is light weight and powerful. There are also available 4-inch and 5-inch fiberglass trimmers which produce one horsepower and are highly effective. The sharper the blade the better.
Put masking tape over the surface of the fiberglass panels to prevent chipping when cutting. A jig saw with a fine metal blade is another option for cutting through hard fiberglass.
Cut the fiberglass using a router, a fine bladed hacksaw, a large hole saw or water jet saws. These are just a few different methods for cutting through fiberglass. Which ever method you choose, just be careful, and follow any manufacturers instructions that come with the product or tool.