In this article, I will be dealing primarily with upholstery foam, but the same techniques will work with EVA foam and other closed cell foams as well.
Foam can easily be cut with a razor blade or scissors. Thicker foam is more easily cut with a serrated knife or even an electric knife like the kind use to carve a turkey. Hot wire foam cutters are also available.
For foam 1″ thick or thinner, razor blades and scissors work great. With thicker foams, you may want to use an electric knife or a foam cutting saw or hot wire foam cutter.
Although scissors are great for cutting 1/2″ foam for puppet making, poly foam will dull the blades of scissors very quickly. I only use old scissors for trimming foam.
Razor blades are my preferred way to cut foam for heads and bodies. They cut straight and quickly. Like scissors, they too will dull quickly, but they are inexpensive and disposable.
For thicker foam, or for cutting a stack of foam hands, I prefer to use my hot wire cutter. With it, I can cut 4 hand patterns in 1/2″ foam quickly, precisely and they all match up perfectly. I have a Hercules Tabletop Foam Cutter that works great. You can get the current Amazon price HERE.
When cutting foam, you will want to get a square edge. Hold your razor blade straight up and down when cutting. If your blade leans to one side, you will get a beveled edge.
To get a square cut with thicker foam, 2″ or more, mark the foam on both sides. Cut about halfway through the foam, then flip it over and finish cutting all the way through.
This works well on thicker foam where it’s harder to keep the cut straight all the way through. You can also cut on curves.
Foam is often covered with fleece or other cloth, so don’t worry too much if the cut looks a little messy, you can use scissors to trim the foam.
If you want to create a rounded edge, or if you want to cut foam professionally, it’s worth investing in a foam cutter like the AccuCutter 350 foam cutter, which has two blades to produce a fine, reliable cut.
HOW TO CUT FOAM WITH A BREAD KNIFE
You know, foam is kind of like bread, a bread that you should not eat, but it’s kind of like bread. It’s bubbly. When they make foam, they put it into a great big bread pan, if you will.
And they cook it and it bubbles up. And the great big piece that comes out before they slice it into pieces, they actually call a bun. So you see there’s a bread analogy.
So if you think about cutting bread, what would you use to cut bread? A bread knife. This is like a bagel knife, a cake knife, any kind of serrated edge type of a knife. Actually the longer the blade, the easier it is to work with.
You can use an electric bread knife or just a plain bread knife.
How do you cut foam? Well, what you need is a Sharpie marker and you want to mark off the line that you want to cut. I have traced my patterns onto my foam. I will then use my bread knife very simply to cut the pieces out.
With thick foam, 2″ or more, what you want to do is you want to score the foam rather than saw the foam.
So to score the foam, you’re just going to go straight across and don’t press too hard, press lighter. It’s better to do a number of light strokes than just one or two heavy strokes. You’ll get a smoother cut.
Depending on how thick the foam is, you can cut right through it. Now, the key thing is you want to make sure that your knife is at a 90 degree angle.
Otherwise, you’re going to have a kind of jagged piece of foam, so make sure you’re keeping it at an even angle and make nice and light strokes, and you can see that it cuts a very smooth, reasonably smooth line.
Foam is going to be under pressure in most cases with the fabric anyway. So you don’t need perfection, but for joining edges you do want them square.
You can also cut a curved line. Now, if it’s a gentle curve, you can still use the same method of scoring and sawing. But if it’s a sharper curve such as a circle, you may have to put your knife at the side and cut up and down, similar to how a jig saw works.
It is a little more tedious and you have got to pay closer attention, but you can still do it. Just do little nibbles at a time, making absolutely sure that your knife is at a 90 degree angle.
Don’t try to cut too much at a time, just a little nibbles and you’ll find even on a somewhat radical curve, you can get pretty good line.
HOW TO SHAPE FOAM
The foam can be shaped in a variety of ways. Professional upholsters will often use an angled die grinder or a drill with an abrasive pad. Those electric powered tools make quick work of shaping foam.
However, mistakes can easily be made and all of a sudden you have a divot rather than a smooth, consistent surface. If you want to avoid those possibilities, you may want to consider making your own shaping tool.
The easiest way to cut a wedge from the side of a block of foam is to use a foam saw. Remember, the more consistent the cut is, the easier it will be to shape the foam.
An alternative is to use an electric kitchen knife that is used often for Thanksgiving dinners. Here it works fairly well. It’s a little bit more difficult to control the blade and it doesn’t cut nearly as well as the foam saw, but it does work.
The electric kitchen knife works fairly well, but you will get a lot more inconsistencies in the foam. This will only work with a medium density or lower density foam.
It will not work well with a high density foam, whereas the blade foam saw, is much more consistent than the electric kitchen knife. And this works with medium density, high density, low density foams and you will get more consistent cuts with it.
Now it’s time to shape the foam
Once you get a basic shape cut out it’s time to shape it. A jar lid works well as a sander. A spaghetti jar lid or other jar lid is all you need to make this tool.
Use a screw put some holes in it. Screw the screws in from the inside of the lid. This will leave rough metal edges on the other side. This is an excellent shaping tool for your foam.
A tool like this actually works quite well because you can’t make a mistake. It is such a slow process. Just come across the foam and shape the edges so they are round.
Now a good cut makes this job much easier because you don’t have to worry about all the gouges he electric kitchen knife might create.
So using a tool like this, you can shape the foam slowly and because it’s not on a tool, it’s nearly impossible to create a gouge in your foam so you can shape foam slowly.
This is almost like being an expert sculptor. That’s basically all you’re doing here is you’re sculpting the foam, making sure that you’re not creating any gouges or indents in the foam as you go and giving it a rounded look.
This tool actually works well with medium density foams and high density foams as long as they’re a polyurethane foam and you can make it yourself,
With a 60 grit sanding block, you can do your final shaping. It’s not going to take off much, but it is going to take off all those loose fibers. It does take off a little bit at a time.
So if you want to do your final shaping and make sure everything still looks good, you can use a sanding block.
If you want to know which foams I use and where I buy them, be sure to check out my resources page HERE.