How to Cut Open Cell Foam: Two Quick and Easy Methods for Great Results

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 jet of water to make precise products. However, not all projects require computer programmed control. Many foam applications require only 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, as cutting foam is the easiest thing since pre-sliced ​​bread.

Approaching foam cutting like you would bread cutting 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 describe the tools and technique you need to cut foam to perfection.

For starters, a flat, stable surface that won’t be damaged by a knife is top priority, both for safety and for cutting. It is important that the entire foam slab fits on the cutting surface, as balancing and supporting the foam hanging off the table while cutting can create sloppy lines and is dangerous. Working on flattened cardboard on the 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 right 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 padded foam 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, make smooth back-and-forth cutting motions through the body of the foam. Let the motion and sharpness of the blade go 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. Electric carving knives, the same ones introduced 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 sawing will cut their way through the foam at their own pace, giving you a cleaner cut than if you forced it in a hurry. The only drawback to using an electric knife is availability: everyone has at least one serrated blade in the house, while 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 has already been alluded to, but it is important to mention it again: it must 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 is impossible to achieve balanced pressure on the foam by hand, leaving a wavy or jagged edge when pressure is released. Cutting correctly only takes a few minutes longer, and you’ll be much happier with the end result when you see 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 slightly exceeding the exact measurements of what you’re doing, the compression of the foam will allow it to fit easily into a cover, leaving it with the full look you want. On foam products like crown molding, this gives you a little room for error, as a less than perfect cut can be compressed and hidden when placed against another piece of trim.