21st Nov 2022 -

Whatever you are using an insulation board for, it’s vital that you cut it to the exact size needed. Insulation boards that are incorrectly cut may not fully cover the area they are insulating, allowing heat to escape from a home. There are several good methods for cutting insulation boards, including using a utility knife, a table saw, and a hot wire cutter in the case of polystyrene boards.

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Cutting Insulation Boards With A Utility Knife

A utility knife is the recommended tool for cutting foam boards by hand, offering a cleaner cut compared to other popular options like a putty knife, a utility knife, or a serrated knife.

Tools Needed

  • Flat Surface
  • Straightedge Ruler
  • Permanent Marker Pen
  • Utility Knife
  • Clamp or Vice (rubberised)

How To Cut Insulation Boards With A Utility Knife

Precisely Measure and Mark Your Foam Board

You should have the exact measurements you’ll need for your board in advance, double-checking the measurements of your joists, cavity, or wall to ensure you are making accurate cuts. You should then use your straightedge ruler and permanent marker to accurately mark out the cuts needed on your board. This should also be double or triple-checked to avoid any errors. 

Secure Your Board In Place

Your board should be placed on a perfectly flat surface, like a workbench. Don’t cut boards on a home table without a protective layer over it, as you risk damaging it. You should clamp your board to the flat surface using rubber clamps or vice while cutting. This will ensure that your insulation board stays in place.

Score Along the Ruler With Your Utility Knife

Place the straightedge ruler exactly on the line you have drawn. Hold the knife close to the ruler, and score along the length of the straightedge ruler using your utility knife, ensuring you follow the line exactly. You do not need to use the blade to cut fully through the board, simply mark it across with a shallow cut. Once you have accurately scored across the board, cut again to get a deeper incision, though you still do not need to fully cut through the board.

Builder installing a foam insulation board on a block wall.

Remove the Clamp and Break the Board Off

Once you have thoroughly cut across your board, remove the clamp or vice from it. Turn the board over, leaning weight on one side of it and bending along the seam. It should naturally break into two, giving you a cleanly cut, accurate piece of foam board.

Cutting Insulation Boards With a Table Saw

Tools Needed

  • Table Saw
  • Straightedge Ruler
  • Permanent Marker
  • Eye and Mouth Protection

How to Cut Insulation Boards with a Table Saw

Measure and Mark Your Foam Board

It’s vitally important for insulation boards to be the correct size for installation, with boards that are too small creating gaps that will allow heat to escape from a house. You should measure carefully and double-check each gap that you will be placing insulation within, before carefully measuring and marking your insulation board, ensuring that it is accurate. Being overzealous at this stage will limit the potential losses that will come from miscutting insulation.

Wear Protection

Cutting insulation boards with a table saw will throw up a lot of dust so you must be fully protected. Using safety goggles and a face mask will shield you from the fine dust thrown up by the table saw. You should avoid wearing gloves while operating a table saw, as they can get caught within the blades. Also avoid wearing anything that might catch within the saw, such as long sleeves, dangling jewellery, or ties.

Guide Your Saw Down the Line

Keeping your hands at least 15cm from the blade, guide the insulation board through the blade, cutting it down the line accurately. Once your board is broken into two, check the side you will be using to make sure the cut is even. If the cut is inaccurate, you can make smaller adjustments with the saw. If it’s accurate, wipe down the side of your insulation board to remove any residual dust.

insulation boards

Cutting Insulation Boards With a Hot Wire Cutter

A hot wire cutter can be used for polystyrene insulation boards, like XPS and EPS boards. In addition to a hot wire cutter, an electric carving knife can be used, though it will be less accurate.

Tools Needed

  • Hot Wire Cutter
  • Straightedge Ruler
  • Permanent Marker

How to Cut Insulation Boards With a Hot Wire Cutter

Measure and Mark Your Foam Boards

Measure the exact specifications for the spaces you will be fitting insulation boards, carefully double-checking each measurement. Then, using the straightedge ruler, mark the correct cutting lines on your polystyrene board, drawing across them with the permanent marker.

Cut Along the Board

Depending on your hot wire cutter, there may be a place to balance your board on the hot wire cutter, allowing you to position it and move the piece of insulation board through the hot wire, accurately and cleanly cutting through the board.

Get the Tools to Cut Insulation Boards Like a Pro

With the highest quality boards and blades that provide clean cuts, Building Materials Nationwide has what you need to complete every insulation job quickly and correctly. Submit any additional questions through our online form, and our team of experts can recommend the right materials for your next project.

For trade professionals, we offer exclusive trade accounts with VIP benefits. Our trade members get their own personal account manager to help with sourcing speciality insulation boards, blades, and hot wire cutters that perfectly suit your specs, tapping into our extensive supplier network. Sign up for discounted trade member pricing on all the top brands of utility knives, table saws, and more for precision insulation board cuts.

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