As an inexpensive, easy to use product, Styrofoam rigid foam insulation is extremely popular with homeowners. I used it myself to add additional insulation to my garage door.
However, one of the messiest parts of the process was figuring out how to cut the Styrofoam insulation.
It’s not as easy to shape, compared to metal or wood. And did I mention it was really messy?
Most homeowners struggle when installing Styrofoam insulation in their homes. So I wanted to share some of my experiences cutting Styrofoam, and some of the best tools I found to do the job with minimal mess.
For the record, Styrofoam is a brand-name (like Xerox or Band-aid), trademarked by the DuPont company.
However, it’s often used to refer to any type of EPS or XPS foam. Even though it’s not technically accurate, I’ll be using ‘Styrofoam’ interchangeably to refer to any type of rigid-foam insulation board.
If you’re wondering what the right foam insulation is right for you, check out my guide to buying the most efficient rigid foam insulation.
How To Cut Styrofoam Insulation
Styrofoam is a good insulation option to increase energy efficiency in your house. It’s perfect for the average DIY-homeowner. It’s lightweight and doesn’t require any special tools or protective clothing to work with it.
What type of tool you choose to use will depend on the shape and use of the Styrofoam insulation.
Below is a step-by-step guide on how to cut the foam.
Before you even start working on your piece of Styrofoam, or rigid foam insulation, it’s important to securely clamp it to your workbench.
Unfortunately, I only figured this out after a few too many messy cuts. Securing the insulation board ensures that it is firmly held to place and won’t shift or slide when marking or cutting.
Most likely, you’ll be working with straight surfaces and edges. I highly recommend using a drywall T-square or long, metal ruler. You definitely don’t want to get the dimensions wrong, especially if you’re working with large pieces of foam board.
Measure the length and width you need to work with, and compare that with the Styrofoam to choose the most suitable place to cut from. Unless you’re making small trimming cuts, you can often get multiple pieces out of one large piece of Styrofoam.
Remember to measure twice and cut once.
Once you have the measurements, use a permanent marker to mark the surface of the Styrofoam. While cutting, ensure that the Styrofoam is resting on a flat surface so that the lines are accurate and straight.
Remember that these lines will guide your cutting. Keep them visible and simple.
The Cutting Process
The cutting process will vary depending on the type of tool you are using. Below are the steps followed when using a knife to cut the foam.
Choosing an excellent tool to cut the foam
There are several knives out there that you can use to cut Styrofoam. However, ensure that the one you chose is segmented. Such blades are ridged along the cutting surface and will therefore give you a clean and clear cut.
Scoring the foam with the knife
Take the knife you chose to use and use it to cut the Styrofoam along the edge of your foam. The cut should not necessarily follow the cutting lines completely but should be along the cutting line itself. Be careful with steps; most people mess it up by cutting carelessly since there will be a second cut.
Making the second cut
Now run your knife carefully along the cutting lines. Most are the times when the foam isn’t cut just by scoring it once using the knife. Make the cuts carefully, ensuring that you precisely cut along the said lines and leave the rest of the Styrofoam intact.
Unclamp the Styrofoam
Once you have ascertained that the foam is well cut and even unclamp it. Do so while examining to check whether the cut is thorough. If you notice that it is not evenly or fully cut, clamp it again and repeat the process. Do not make the mistake of trying to cut the remaining part manually.
Using Circular Saws
I recommend the use of circular saws when making a lot of cuts for insulation sheets.
Preparation to cut
Cutting a foam using circular saws might pose a risk to your eye safety due to the foam fragments released during the process. Therefore, you are required to wear goggles.
The Cutting Process
When insulating your home, you will be using 2-inch Styrofoam most of the time for maximum insulation. This, therefore, makes the circular saw an ideal tool to use since you will need to cut a lot of sheets.
To begin with, support your Styrofoam sheet by clamping it to the surface. After ensuring you made it firm, you can now draw your lines concerning the required dimensions. Once you have already marked the Styrofoam along the desired lengths, ensure that there is no foreign material along the said cutting lines and begin your cutting.
The blade will cut through this material effortlessly, but you have to be careful with your cut. You can set your blade to its maximum cutting depth for the best cuts.
However, it is essential to note that you can’t cut curves on the Styrofoam using circular blades. In such a scenario, you will have to rethink your option and go for the one that easily does that, such as a jigsaw.
The Best Tools to Cut Styrofoam
Now that we know the basic process of cutting foam board insulation, which tools should you use?
It largely depends on personal preference, and the type of cutting you’ll be doing. Here are a few different types of Styrofoam cutters, so you can find one that fits you best.
Best Foam Knife: Klein Tools Combination Duct Knife & Wire Cutters
I’m not usually a fan of combination tools, but I’m making an exception for the Klein Duct Cutter\Wire Cutter combination knife.
To be fair, I don’t use the wire-cutters at all. I have dedicated KNIPEX wire cutters that do that job.
But one of my favorite features about the Klein duct knife is the handle design, and that wouldn’t be the same without the knife also being wire cutters.
I always found single-function insulation knives to be hard to hold. The handles were too thin, so I never felt like I got a good grip on the knife.
Especially when I’m trying to punch through Styrofoam.
Not so with the Klein handle. Even if you never use the cutter feature, the extra width of the grip really makes it easy to hold, and get leverage when you’re cutting.
The 4.6″ blade is double-edged, stainless steel, which makes it more resistant to rust and oxidation. I would have preferred if one side of the blade was serrated, but it’s not a deal-breaker.
Still, the blade is plenty tough enough to cut through foam-board insulation, making your work a lot easier. It also comes with a leather storage sheath to help protect the blade.
- All-steel double edge blade and built-in wire cutter
- Comfortable, contoured grips cover hardened steel handles
- All-steel construction and nickel-chrome plated hardware
Best Handheld Foam Cutter: Woodland Scenics Hot Wire Foam Cutter
Sometimes, simple is all you need.
Woodland Scenics is a company that makes accessories for scale model trains, like scenery, figures and vehicles. Hobbyists use hot wire foam cutters to sculpt the mountains out of foam blocks. This particular cutter is best known for its ability to make clean and precise Styrofoam cuts with minimal fuss.
If you’re not familiar with hot wire cutters, they’re exactly what it sounds like.
They’re simple tools; basically a U-shaped prong at the end of an insulated handle. Between the ends of the prong is a wire. When you plug the tool in to a standard AC outlet, current runs through the wire and heats it up.
You’re literally cutting through Styrofoam like a hot knife through butter.
It has a cutting width of 4.5 inches and a depth of 6 inches, making it ideal for trimming off the excess or for cutting curved edges that would be difficult with a knife. However, because of it’s design, you won’t be able to use it when you’re trimming off more than 6″ of foam insulation.
The handle has a dedicated on\off switch, so it won’t constantly heat up like a soldering iron does. It comes with a power cord attached to the end of the handle. Once plugged in, the wire heats up instantly and doesn’t leave small chunks of foam behind after you cut.
RIDGID Best Tabletop Foam Cutter: Proxxon Hot Wire Cutter THERMOCUT 115/E
If you like the idea of a hot wire cutter, but the Woodland Scenics handheld tool isn’t big enough, then the Proxxon THERMOCUT is the answer.
This tabletop hot wire cutter works on the same principal. Heat up a wire and it’ll cut through Styrofoam insulation like it’s butter. However, the Proxxon Hot Wire Cutter THERMOCUT 115/E has a full 13 3/4″ cutting area, double the size of the handheld tool.
Like a table-saw, this tool has a large, weighted base that allows you to manually feed longer pieces of foam through the cutting wire. That makes it ideal for larger pieces of foam-board insulation.
For more exact measurements, it also has a 1 cm squared box grid printed out on the surface. There’s also a built-in protractor on the edge which comes in handy when want to cut shapes freehand. They’re a nice touch, but it’s still recommended to use a dedicated analog or digital measuring tool to get the right angles.
There’s a heat adjustment knob on the front panel to change the temperature of the cutting wire. When the wire gets too hot, it tends to cut unevenly and might end up destroying your foam insulation. On the other hand, if the wire cools down too much, it will slow or even stop the cut.
The cutting temperature is adjustable between 210 degrees F and 390 degrees F. It’s worth noting that it takes some trial and error to get the right temperature. I recommend having a scrap piece of foam-board insulation handy to practice on before trying it out for real.
- Cutting wire temperature 360° Fahrenheit for clean cuts
- Double function fence with lockable feed bar
- Working surface of Alu Cobond compound for ease of pushing work pieces
- Printed grid and protractor are applied to the base
Best Foam Saw Blade: Bullet by Marshalltown Foam Blade for Circular Saws
If you already have a table saw, then the best (and cheapest) option is to get a replacement blade that’s designed specifically for foam. I’m a big fan of Marshalltown tools, having used them extensively on my drywall project. So their dust-free foam blade was a natural choice.
Made under Marshalltown’s Bullet Tools line, this still has all of the great build quality you’d expect from Marshalltown tools.
Because it attaches to your existing table-saw, you’ve got the ability to cut large sections of Styrofoam, without being limited by your cutting tool.
Made from carbon steel, the blade comes in either 7.25″ or 8.25″ sizes. Both are coated with high-performance ceramic, designed to keep the heat on the cutting surface for smoother cuts. It also helps eliminate up to 95% of static foam dust, to help keep your garage clean while you’re cutting.
Unlike the other cutting tools on this list, the saw blade cleanly slices through foam-board, rather than melting or sawing it. That means less debris and cleaner cuts. Additionally, it also allows the foam blade to cut through both paper and foil-backed foam insulation.
- Razor sharp, Carbon Steel slices through foam without producing dust
- Thermal break design concentrates heat on the cutting edge for a factory quality cut
- Cuts EPS (Expanded Polystyrene/White/Bead Board/r-tech insulation) foam, XPS (Extruded Polystyrene/Blue/Pink) foam, Poly-Iso (Polyisocyanurate/rmax insulation) foam, Foil or felt faced foam, and cuts handi foam/seal