The Best Ways to Cut Styrofoam for Crafts, Insulation & More

Whether you’re working on a craft or a home renovation project, cutting styrofoam without making a mess takes a little finesse. Luckily, there are a lot of tools and easy tricks to make slicing through styrofoam a lot easier. Keep reading, and we’ll walk you through how to use tools like a utility knife or hot wire cutter, and how to stay safe while doing it, plus tips from cosplayer Steven Geary and licensed contractor Lui Colmenares to make the job easier.

Easiest Way to Cut Styrofoam

Foam cutting expert Steven Geary says to use a hot wire foam cutter, utility knife, or jigsaw to cut styrofoam. Here’s how to do it with a utility knife:

Mark a line with a pencil or marker.
Extend the blade of a utility knife and hold it at a low angle to the foam.
Using a straightedge as a guide, make a shallow cut in the foam with the knife.
Cut through the foam multiple times with light pressure for a clean, smooth edge.

Section 1 of 7:

How to Cut Styrofoam with a Utility Knife

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Hold a ruler along the line you want to cut. Use a pencil to mark your cutting line. Line up a ruler or another straightedge along the line and hold it down firmly so it doesn’t move or shift around while you’re making your cuts.^{[1]
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- Set the foam on a workbench, cutting board, or cutting mat to prevent the blade from accidentally damaging the surface below.
Meet the wikiHow Experts

Steven Geary is a cosplayer with over 8 years of experience. He’s also a content creator under the handle Omega Shrine, where he specializes in tutorials on cosplay and costuming techniques.

Lui Colmenares is a licensed contractor and handyman for Mr. Handy NYC. He specializes in carpentry, painting, and general handyman work.
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Drag the blade through the foam with medium pressure. Extend the blade of your utility knife as far as it can go. Hold the blade low and close to the foam. Apply light pressure as you guide the blade along the line, using your straightedge as a guide.^{[2]
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- Utility knives work best for cutting foam boards that are thinner than the blade’s length.
- Avoid holding the blade at a high angle or pressing hard into the foam because it will create jagged edges instead of a clean cut.
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Don’t try to slice completely through the foam on your first pass. Instead, keep applying light pressure and making slow, shallow cuts so the edges stay smooth. After a few passes, the blade will pop out the other side without making a mess.^{[3]
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Section 2 of 7:

Cutting Styrofoam with a Saw

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Mark the line you want to cut. Draw a line with a pencil or marker where you need to make your cut. Line up a ruler or another heavy straightedge (like a piece of lumber) along the line to use as a guide while you’re cutting. Then, make sure the piece you’re cutting overhangs the edge of your work surface.^{[4]
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- Saws work best for thicker pieces of styrofoam because they have a longer cutting blade.
Put on a dust mask and safety glasses. Both hand saws and electric foam saws create a lot of dust and loose styrofoam particles. Protect your eyes and lungs from all of the debris by wearing a mask and glasses the entire time you’re working.
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Saw slowly along the marked line. If you’re using a hand saw, hold it at a 45-degree angle at the edge of the foam. Slowly move the saw up and down to start cutting through the foam.^{[5]
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Research source} If you’re using an electric foam saw, position the blade along the edge so the guard rests on the foam. Use a slow, steady speed as you follow the line until you cut all the way through the styrofoam.^{[6]
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- Electric saws made specifically for foam can cost over $200 USD, so check if your local hardware store offers equipment rentals so you don’t have to buy one.
- If you don’t have a saw, use a serrated bread knife or an electric carving knife in a pinch.

Section 3 of 7:

How to Cut Styrofoam with a Hot Knife

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Hot knives work well for cutting straight or curved lines through styrofoam without leaving behind any mess. Draw the shape you want to cut with a pencil or marker to use as a guide.
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Preheat the hot knife. A hot knife plugs in and warms up the blade so it melts the styrofoam while you’re cutting. Plug the hot knife into an outlet and turn it on. Give the knife a few minutes to warm up until it starts steaming.^{[7]
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- Trying to cut the foam while the blade is still cold may leave jagged or messy edges.
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Push the hot knife through the foam to slice along the line. Once the knife is fully heated up, push it into the foam until it comes out the other side. Slowly move the blade along the line you drew. Keep the blade moving so it doesn’t melt or burn any of the edges. When you’re finished cutting, pull the knife out and turn it off so it can cool down.^{[8]
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- Melting the styrofoam creates harmful fumes, so be sure to work in a well-ventilated area and wear a respirator.

Section 4 of 7:

Cutting Foam with a Hot Wire Cutter

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Mark the lines you want to cut on your piece of styrofoam. Hot wire cutters work best for cutting lines through styrofoam of any thickness, but they are especially good for rounded edges and curves. Use a pencil or a marker to draw the cut lines on your styrofoam.
- Geary prefers using a hot wire foam cutter when working with styrofoam. “It’s a heated wire that cuts through the foam like butter. The ones with a variable temp are my preference since it gives me a little more control on how fast it melts through.”^{[9]
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- Another perk of using a hot wire is that “there isn’t much ‘debris’ from the foam particles,” Geary adds.^{[10]
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Tighten the wire and plug in the cutter. Hot wire cutters connect to power and heat a nichrome wire so it can melt through styrofoam. If the wire isn’t already attached, pull it tight between the metal prongs and secure it with the clamps. Then, plug the cutter in and let it preheat for a few minutes.^{[11]
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- Many hot wire cutters are handheld, but other, more expensive models attach to a table or stand to cut thicker pieces of foam.
- Avoid using the wire cutter while it’s cold because it will not cut through the styrofoam as easily.
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Guide the hot wire along the cut line. Once the wire is hot, apply slow, consistent pressure with the cutter along the desired cutting line. Move the wire slowly because moving too fast through the foam will cause the wire to snap. When you’re finished, unplug the wire cutter and let it cool down completely.^{[12]
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- Be careful not to touch the wire because it’s extremely hot and could cause burns.
- If you have a hot wire table, then push the foam slowly through the wire to make a clean and consistent cut

Section 5 of 7:

How to Cut Polystyrene Insulation

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Cut through the insulation with a utility knife for the cleanest cut. Extend the blade on your utility knife as far as it can go. Hold a ruler along the line you want to cut. Hold the blade as close to the foam as you can and apply gentle pressure as you drag it along the line.^{[13]
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- Continue making shallow cuts through the insulation until you completely cut through the styrofoam.
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Use a circular saw for an easy, quick cut. Colmenares recommends using a 4–4 ¹⁄₂ in (10–11 cm) blade to cut rigid foam insulation boards.^{[14]
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Lui Colmenares
Licensed Contractor

Expert Interview} Mark the cut line and position the board so it overhangs a work surface. Slowly guide the blade along the line until you cut all the way through the foam.
- Wear safety glasses and a dust mask when you use a circular saw because it creates a lot of foam particles that could irritate your eyes or lungs.
- Run a vacuum next to your workstation to help suck up any dust and debris from the cut.
- If you don’t have a circular saw, a handsaw works well as a replacement.

Section 6 of 7:

How to Cut Styrofoam Balls

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Divide round styrofoam balls by cutting them right down the middle. Trace a line along its equator with a sharp pencil, which is usually already marked by the manufacturer. Slowly work your tool through the foam so it creates a clean cut without any jagged edges.
Try using dental floss or embroidery thread. Secure the ball to a work surface or have another person hold onto it. Cut off a long piece of floss or thread. Make a small indent in the foam where you want to cut it, and place the thread in it. Then, pull the thread tight, and make gentle back-and-forth sawing motions into the foam. Work the thread slowly through the foam until you cut all the way through it.^{[15]
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Section 7 of 7:

Safety Precautions for Cutting Styrofoam

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Wear safety glasses and a mask. Styrofoam debris and fumes can irritate your eyes and lungs, so protect yourself the entire time you’re working. Before you make your first cut, put on your safety glasses and dust mask and leave them on until you’re finished.^{[16]
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- Geary cautions, “If you’re using a hot wire cutter, wear a respirator! The fumes aren’t safe to breathe and can be harmful over prolonged periods.”^{[17]
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- Geary adds that you don’t need a respirator if you’re using a tool like a box cutter or jigsaw, but that you should still wear a mask: “The little particulates can be annoying, and [you] don’t want to accidentally breathe any in.”^{[18]
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This is especially important if you’re using any electric tools that melt the styrofoam because they produce fumes. Choose a spot that has good airflow, such as a garage or a room with open windows. If possible, work outside so fumes don’t build up.
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Clean any debris when you’re finished. Cutting styrofoam usually leaves behind some dust or debris, even when you use the cleanest methods. Take some time to vacuum up any residual styrofoam you see around your workspace when you finish so that it doesn’t spread around.
- Geary says that “there’s always some level of a mess” when you’re working with styrofoam, so “try to do it in an area that [you] can easily sweep or run the shop-vac.”^{[19]
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Community Q&A

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Why do I need to wax the knife?

Community Answer

Think of the wax as a lubricant, it allows the knife to go through the product faster.

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Can I smooth the surface with a fine grit sand paper?

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Not a good idea. Even a fine grit will tear the foam: think rough sand against a very smooth surface. Instead, use a spare piece of foam get rid of the burs. Just rub the foam piece gently against the cut edge.

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Can I use a kitchen knife to cut Styrofoam?

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Yes, and the ones that work best are the ones with a serrated blade.

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Tips

If you want to make creative styrofoam shapes for crafts, try using different cookie cutters. Press them into thin pieces of foam to perfectly cut out the shapes.

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Cut the styrofoam outside if you can to avoid making a mess indoors! Try to work in an area shielded from wind so the pieces don't fly around all over your yard.
If you use a hot knife, you will not get any of the styrofoam shavings everywhere.

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