How To Cut Foam Board Insulation

By Dan WienerLast update
How To Cut Foam Board Insulation

Foam board is a great insulating material for different spaces, including ceilings, interior walls, exterior walls, and rectangular ducts. It is moisture-resistant, therefore, ideal for use in mildew-prone areas or areas with high humidity.

Learning how to cut foam board insulation is a simple process if you know the right steps. Even with amateur handyman skills, almost anyone can do it! You need to cut it to the right size to fit the space you want to insulate. There is a wide range of tools you can use to cut depending on what you have easy access to and the size of your foam board.

This article provides you the steps and tools for cutting your foam board insulation. Read on to learn more about each step.

Steps For Cutting Foam Insulation

Steps for Cutting Foam Insulation
Image Source: Miljan Zivkovic

Tools

  • Worktable
  • Cutting tools: Utility or putty knife, circular table saw, or jigsaw
  • Safety goggles
  • Felt tip marker or pencil
  • Vise or rubber clamp
  • Dust mask
  • Drywall square or straight edge ruler
  • Tape Measure
  • Your foam insulation board

Instructions

1. Measure The Dimensions Of The Installation Site

Using a tape measure, measure the length and width of the specific installation site of the foam insulation board. Put it down on paper to avoid forgetting. It is best to confirm the measurements at least twice to ensure you have the right dimensions.

2. Lay The Foam Board On The Worktable Or A Flat Surface

Identify a flat surface to work on. You can use a worktable or any other flat and smooth surface. Should you choose to use one of your home tables, place a protective shield down to protect it from cuts or scratches. Laying the foam insulation board on a straight surface enables you to make precise cuts easily.

3. Mark Cutting Lines On The Foam Board

Transfer the dimensions you measured during step 1 onto the foam board using the drywall square or straight edge ruler. Place the straight edge ruler on the foam board and mark the dimensions using a felt tip marker or pencil. Before using your cutting tool, double-check the marks for accuracy. It is better to have the measurement too large by a few inches than to have it too small, as you can always trim down the excess foam. It will be a lot harder to add a few inches of foam.

4. Clamp The Foam Board On The Flat Surface

You can clamp the board against the table using a vise or rubber clamp to keep it in place when cutting. If using rubber clamps, clip the first one onto one corner and the other onto the diagonally opposite corner.

5. Wear Protective Gear

Before you start using your cutting tool, put on your goggles and dust mask. Depending on the tool you are using to cut, the foam sheet may produce dust particles that could get to your eyes, nose, or mouth. You may also wear some gloves.

6. Cut The Foam Board

This section will discuss the various methods of cutting the foam sheet depending on the cutting tool you have at your disposal.

How To Cut Foam Board Using A Utility Knife

A utility knife or craft knife is one of the most affordable and accessible tools, even for amateur DIY-ers. If you do not already have one, you can buy a craft knife at a hardware store near you or Amazon.

Go for a segmented blade utility knife as it offers an adequate blade length for cutting through the insulation foam. It is the best tool to use if you are cutting thin foam board. It makes a thin, smooth cut.

Here are the steps for cutting foam board insulation using a utility knife:

  1. Hold the utility knife firmly in your dominant hand.
  2. Score the insulated foam, then run the knife along the marked cutting line in a smooth continuous movement. Lean more towards the outer edge of the marked line than the inner side to avoid cutting into the installation dimension of the foam.
  3. Make a second cut through the first incision to separate the foam boards fully.
  4. Unclamp the foam sheet and inspect it for an uneven surface. If you are satisfied with the cut, put it aside in preparation for installation.

How To Cut Foam Board Using A Circular Saw

A circular saw is most ideal for cutting thick foam boards. For example, if you need to cut several thin insulation boards to cover a larger insulation area, you can pile 2-3 foam boards and cut them simultaneously using a circular saw. However, this method produces a lot of dust and foam particles. Therefore, wear your goggles and dust mask properly.

Here are the steps for using a circular saw.

  1. Clamp the foam board, so the marked cutting line is outside the edge of the flat surface beneath. Allow at least an inch away from the edge of the worktable or flat surface to provide enough clearance for the circular saw when cutting.
  2. Plug the circular saw into an appropriate power source as per the manufacturer’s recommendations.
  3. Rest the foot of the circular saw on the foam board, making sure the blade is aligned with the marked cutting line.
  4. Set the blade to full length.
  5. Pull the trigger and allow a few seconds for the blade to run at full speed.
  6. Run the blade smoothly and slowly through the foam board as you guide the saw through the cut line. Do not push the circular saw too fast and allow ample time for the blade to cut.
  7. Once the cut is complete, release the trigger and allow the table saw blade to stop running. Then, power off the circular saw and put it aside.
  8. Pick up the cut foam board, dust off any foam particles, and inspect it to ensure it meets your required measurements. Then, put it aside in preparation for installation.

How To Cut Foam Board Using A Jigsaw

A jigsaw is also effective for cutting thick foam boards. However, it produces foam particles and clouds of dust, which necessitates wearing protective gear. Here are the steps for using a jigsaw to cur foam board.

  1. Securely, clamp the foam board a few inches past the marked cutting line to allow enough clearance for the jigsaw when cutting. A jigsaw exerts quite a bit of force on the foam, so ensure that it is tightly clamped.
  2. Install a thin, finely serrated blade of standard length into the jigsaw.
  3. Plug the jigsaw into an appropriate power source as per the manufacturer’s recommendations.
  4. Rest the foot of the circular saw on the foam board with the blade aligned with the marked cutting line. The blade should not be touching the foam until the jigsaw is running.
  5. Pull the trigger and allow a few seconds for the blade to run at full speed.
  6. Gently pull the jigsaw through the foam board to make the cut.
  7. Once the cut is complete, release the trigger and allow the blade to stop running. Then, power off the saw and put it aside.
  8. Pick the cut foam board, dust off any foam particles, and inspect it to ensure it meets your required measurements. Then, put it aside in preparation for installation.

Conclusion

A foam board offers excellent insulation to save you energy costs. However, cutting it into the right dimensions is crucial for ensuring its efficiency. As discussed above, there are various tools you can use to cut your foam board. Choose according to the thickness of the board, your budget, and the accessibility of the tools.