Like many things you’ve never tried before, cutting foam can be daunting. Foam die-cutting services can produce tens of thousands of identical parts, while waterjet technology uses a 0.005-inch diameter waterjet to manufacture precise products. However, not all projects require computer programmed control. Many foam applications only require a few short, straight cuts. For these jobs, cutting your own foam at home is not only the cheapest option, it’s also the easiest.
However, the last thing anyone wants to do is make an inexperienced mistake and ruin a new foam insert or mattress topper. Fortunately, this fear is unfounded, since cutting foam is the easiest thing since pre-sliced bread.
Approaching cutting foam as you would cutting bread is a great idea, as the similar textures make the cutting method virtually identical. And if you associate work with something familiar like bread, suddenly the project becomes a lot less intimidating. In fact, having the right tools for the job is more important than any previous foam cutting experience. These next few paragraphs will outline the tools and technique you need to cut the foam to perfection.
For starters, a flat, stable surface that won’t be damaged by a knife is the top priority, both for safety and for cutting. It is important that the entire slab of foam fits on the cutting surface, as balancing and supporting the foam that is hanging off the table while cutting can create sloppy lines and is dangerous. Working on flattened cardboard on your basement or garage floor is a smarter choice than a sturdy but too small workbench.
While using a proper work surface is important for safety, the proper cutting tools will give you the cleanest lines and edges for your project. There are two types of knives that work well for cutting open cell foam padding at home: both should be as sharp as possible, but neither should have straight blades.
The first option is a standard serrated carving blade or bread knife. As mentioned above, cutting foam is like cutting bread, so it makes sense that the same type of knife would work well for both materials. When cutting with a serrated blade, use smooth back and forth cutting motions across the body of the foam. Let the movement and sharpness of the blade cut through the foam, not forceful pressure. With a sharp blade and smooth cuts, you’ll cut through foam effortlessly. Start cuts at the edge of a foam sheet whenever possible and cut at a 45 degree angle. With a little time and care, you’ll end up with a flush edge you didn’t think you were capable of!
The second cutting method is surprising to many people, but it works exceptionally well. Power carving knives, the same ones that show up every year at Thanksgiving, provide exceptional control and are very similar in principle to the industrial saws manufacturers use to professionally cut shapes and designs. The edge of an electric knife and automatic serration will cut its way through the foam at its own pace, giving you a cleaner cut than if you were to force it in a hurry. The only drawback to using an electric knife is availability – everyone has at least one serrated blade lying around the house, whereas an electric knife may require a special trip to the store.
In addition to the cutting surface, tools, and technique, there are two final things you need to know in order to cut foam like a pro. The first one has already been alluded to, but it is important to mention it again: it should never Compress the foam when cutting. Some people think that with the compressibility of the foam, they can flatten it and cut it with a single slice. The problem with this idea is that it’s impossible to achieve even pressure on the foam by hand, leaving a wavy or jagged edge when the pressure is released. Cutting properly only takes a few more minutes, and you’ll be much more satisfied with the end result when you see the straight edges.
The other tip is to cut around the lines on the foam. To replicate a shape, you need to trace it onto the new foam sheet. Once your design is marked on the foam and you are ready to cut, always do so on the outside of the guide lines. Even if that means you’re slightly exceeding the exact measurements of what you’re making, the compression of the foam will allow it to easily fit into a cover, leaving it with the full look you want. On foam products like crown molding, this gives you a little margin for error, as a less-than-perfect cut can be compressed and hidden when placed against another piece of molding.