There are several different ways to cut foam rubber. The method you choose depends on the thickness of the foam rubber and the amount you need to cut. For small jobs, a simple utility knife may be sufficient. For somewhat larger jobs, an electric carving knife makes a good choice. For very large jobs, you may wish to use a band saw.
How to Cut Foam Rubber
Using a fine-tip felt marking pen, sketch out the design you wish to cut directly on the foam rubber. Use a straight edge to make straight lines.
When cutting foam rubber less than 1-inch thick, press the foam with your fingers and make a succession of small, shallow cuts with your utility knife. As one area is cut, move your fingers and compress the next. Continue until the entire pattern has been cut.
Thicker pieces of foam rubber, up to approximately 3 to 4 inches thick, may be cut with an electric carving knife. Put the thinnest and sharpest blade you have on the knife. Start the knife before touching it to the foam rubber to prevent ripping. Hang the areas to be cut over your cutting table and slowly run the knife around the traced design.
To cut even thicker pieces of foam rubber, use a band saw. Start the band saw and slowly push the foam rubber into the blade, following the line of the pattern you have drawn.
If necessary, you can compress the foam rubber with small pieces of thin board and clamps before running it through the band saw. This can be a good idea if you are cutting more than 6 inches of foam.
The more dense the foam rubber, the easier it is to cut. Very light and fluffy foam rubber can be very difficult to cut and almost always requires the use of a utility knife.
Use caution when using any electrical cutting tool. Wear eye protection when using a band saw.