How To Cut Rolls Or Batts Of Insulation

Disclosure: We may get commissions for purchases made through links in this post.

Fiberglass insulation materials are mainly composed of spun or blown molten glass into fibers and are known to be a very flexible and energy-efficient material to work with. It is also quite cheap and easy to install on your own. If you're planning to do it by yourself, you might be wondering how you can cut rolls of fiberglass insulation to work with for your home improvement project. Here are the steps on how to do it.

How to cut fiberglass insulation batts:

  1. Prepare your materials for cutting: a sharp utility knife, a straight edge wood plank, and a scrap piece of plywood, as well as safety gear.
  2. Lay the insulation on the scrap plywood with the kraft paper side down. Measure the length of insulation that you need.
  3. Place the straight edge wood plank on the insulation right where you want to cut it. Kneel on the plank to compress the insulation and cut through it completely with your sharp utility knife.

Of course, there are also other ways to cut fiberglass insulation. Continue reading to learn more about it because we have compiled all the necessary information you should know.

A man in protective clothing and face mask cuts the glass wool for insulation of walls in an unfinished building, How To Cut Rolls Or Batts Of Insulation

Easy Way to Cut Fiberglass Insulation

Fiberglass insulation is typically available in different forms like loose fill or rigid boards, but in most cases, it is available in blanket form or batts. These fiberglass batts come in different thicknesses, depending on your project needs.

Because this form of fiberglass insulation is readily available in Home Depots and hardware stores, a lot of homeowners decide to install them on their own for their home improvement projects.

Professional workman installing thermal insulation layer with fiberglass wool

Before getting started on installing your insulation, make sure that you have your insulation materials cut to size. This is to ensure that you will be able to cover all the areas that need insulation, with a little extra on all sides to keep it in place. Following this method will help you continue the project with ease.

Before starting out on this process, make sure that you have all the necessary tools you will need to cut your insulation batts precisely. One important tool used in cutting insulation is a high-quality heavy-duty utility knife with snap-off blades.

Get this utility knife on Amazon.

Here are the steps on how you can cut your fiberglass insulation easily.

How to Cut Fiberglass Insulation

Materials Needed:

  • Heavy-duty utility knife
  • Scrap plywood board (wider than the width of your insulation)
  • Straight-edged wood plank
  • Tape measure and marker
  • Cut-resistant gloves and other safety equipment (dust mask, eye protection, etc.)

Steps on Cutting Fiberglass:

  1. Before cutting your fiberglass insulation, make sure to put on protective equipment. Fiberglass insulation can be harsh on skin and may release dust when cut, so it is best to cover up and set up your workspace outdoors.
  2. Lay down your scrap plywood flat on the ground. Make sure that your plywood is wider than your insulation on the top and bottom.
  3. Measure your insulation batt according to size. You can make small marks on the batt to mark the desired length you wish to cut.
  4. Position the straight-edged wood plank's edge on the marks you made, and make sure that your plank is perpendicular to your insulation batt to prevent cutting your insulation unevenly.
  5. Kneel down on the plank to compress your insulation batt and lean forward to press on the other end with your free hand. Make sure that the insulation is as flat and compressed as you can make it.
  6. Hold your utility knife at a 45° angle over the cutting mark, right on the very edge of your plank. Pull the blade straight towards you, using the plank's edge as a guide. Remember to put pressure while cutting and do it in one single stroke. You can clean up the spots that didn't go all the way through afterward.

Get this roll of fiberglass insulation on Amazon.

Are There Other Ways to Cut Insulation?

Cutting an insulation batt with a utility knife is the easiest and quickest way to do this job. However, you may be wondering if there are other methods to do this, especially if you have insulation batts that are thicker than usual.

You might also want to cut insulation into more specific shapes, so here are some other methods you can do to cut insulation batts.

Cutting With A Carving Knife

  1. Pick a carving knife that is at least 7 inches (18 centimeters) long with a very long cord. Make sure that it is clean and sharp, and that the blades are working properly.
  2. Hold up your insulation to a standing position in order to assess the part you will be cutting. Do this on a table with scrap plywood underneath your insulation. Make sure that you have plenty of room to work with between your hand and the knife.
  3. Position your knife perpendicular to your insulation. Rest the knife on the edge of the insulation and hold it straight.
  4. Turn on your carving knife and hold it steady as you cut through the insulation. Make sure that you are not compressing your fiberglass because this may result in an uneven cut. Simply let your carving knife do its job by keeping your hand steady while cutting through the thickness at a steady pace.

Trimming Insulation With Shears

  1. Pick a sharp pair of heavy-duty metal shears. Those that come with thick, serrated, stainless steel blades work best for cutting through fiberglass insulation.
  2. Put a wood board or plank right to the very edge of the insulation where you want to cut it. Just like cutting through with a utility knife, you should compress your insulation batt using this board.
  3. Kneel on the end of the board and press down on the other end with your free hand. Cut through the insulation batt using your metal shears by using the edge of your wood board or plank as a guide.

Can You Split Insulation in Half?

On some occasions, your insulation batt may get in the way around wires and pipes. Typically, some people may want to simply mash their insulation around wires and pipes to make them fit. This method, unfortunately, causes the insulation to lose its R-value.

The best way to work around this issue is to split your insulation batt to half of its thickness. You can simply slide the batt behind the cable or pipe and lay down the other half on top of it.

You can also do this split-and-cut method when insulating around electrical boxes or areas where your insulation encounters obstacles. Avoid squishing your insulation and creating gaps during installation because it may affect the area you are insulating.

Do not pack your insulation in areas like window and door gaps—just fill it loosely with your insulation or use a different insulating material (like foam spray insulation) to do the job.

Foam window insulation on wooden construction

Can You Put New Insulation Over Old Ones?

Sometimes, you may feel that your home is in need of more insulation. A lot of homes usually have layers upon layers of insulation in their attics and walls, and you might be wondering if you should remove them or if you can just add new ones on top if you are planning to do a home improvement project.

The quick answer to this one is yes, you can put new insulation over old ones.

Adding new insulation to your old is a quick and easy way to upgrade your home's insulation. However, there are certain conditions that must be met before you can layer a new one on your current insulation.

Before installing new insulation, make sure that the old insulation is not wet or appears to have been wet at any given point in time. This is because moisture trapped in insulation layers can cause other issues like mold, mildew or it can cause rotting of wood rafters.

Strips of pink fiberglass insulation in a wall of a new building

Final ThoughtsMedia

Cutting fiberglass insulation batts is pretty easy and can be done right at home. All you need is a good utility knife and wood planks that can serve as your guide to cutting your insulation.

You can also use other tools like carving knives and metal shears to cut through your insulation batts. With these methods, you will be able to cut through your fiberglass insulation batts with no problem each time.

Professional workman installing thermal insulation rock wool under the roof

Are you looking for more information about fiberglass insulation for your home? We may have a few articles that might interest you:

Can You Mix Fiberglass And Cellulose Insulation?

How Long Does Fiberglass Insulation Last?

Leave a Reply