Closed-cell foam is a unique material, that, in its various formulations, is durable, resilient, and can be found in blocks and sheets, or thicknesses so thin it behaves like fabric. Because of this versatility, people routinely find uses for it in their everyday lives. However, having foam custom-cut every time you have a need is unrealistic. Fortunately, closed-cell foam is an incredibly easy material to work with. Whether you’re making pipe wraps, packaging, weather stripping, or something else, you’ll need to know how to cut closed-cell foam accurately. By taking the following steps into consideration, you should be able to cut multiple closed-cell foam materials easily.
NOTE: These instructions exclude expanded polystyrene (EPS), which is best cut by hot wire.
Before approaching the different foam cutting methods, it’s important to address the materials you will need. Unlike open-cell foam, closed-cell materials should be cut with a straight, non-serrated blade like a utility knife or crafting knife. These knives work well because their blades are disposable and easy to replace as they dull. Scissors may also be used for smaller, informal projects, though they’re only effective on particular foam types and thicknesses. It’s smart to have a straight-edge to cut by as well. Lastly, always cut foam on a stable surface that won’t be damaged.
Cut: Neoprene, Cross-Linked Polyethylene, Gym Rubber, and Polyethylene Roll
Neoprene is a rubbery material, cross-linked polyethylene (XLPE) is slightly “plasticy,” polyethylene roll is a thin, sheet-like material similar to XLPE, and gym rubber is spongy, but can be the softest or firmest material among these four types depending on formulation. Despite these differences, the physical structures of these materials are similar enough to approach them in the same way when cutting.
When dealing with neoprene, gym rubber, XLPE, or polyethylene roll, the first thing you need to consider is material thickness. If you’re working with sheets 1/8″ thick or less, you have the option of cutting with sharp scissors. Scissors are only suggested for recreational projects because they can leave jagged edges. If you’re making shapes for bath toys, or trimming backing for card making, scissors are fast and effective. Because of its flexibility, PE roll is the easiest material out of these four to cut with scissors.
Single-Pass Cutting Method
For precise projects that involve materials thicker than 1/8″, you will want to cut with a straight blade. Thickness needs to be considered again, as it will dictate the method you use to cut with the knife.
If you’re cutting a sheet 1/2″ or less, you should use the single pass-through method, where you make a single blade stroke that slices through the full thickness of the material. Simply follow your pattern down the foam until you have the cut you want. The single-pass method ensures the cleanest edges, though it isn’t suggested for foam thicker than 1/2″, as it becomes difficult to move the blade through the material smoothly. Using the sharpest blade possible is vital for the single-pass method, as dull knives can snag once you get into the heart of the material.
To make your cut, make sure the foam is anchored at the start of the cut to prevent the material from puckering under pressure. Begin cutting from an outside edge whenever possible and do not stop cutting once you have begun.
Multiple-Pass Cutting Method
For closed-cell foam greater than 1/2″ thickness, it becomes difficult to pull a blade through the material in a single pass. Attempting to do so can leave snags or sloppy cuts. Fortunately, the multiple-pass cutting method will get the job done well on thick sheets of closed-cell foam. Using a straight-edge that runs the full length of the cut is the most important aspect of this strategy, as you will need a guide line to follow as you make multiple slices through the foam.
Once your cutting line is established and your straight edge is in place, begin your cut exactly how you did in the single-pass method. But instead of plunging the blade all the way through the foam, only cut about 1/8″ to 1/4″ of the way through; just enough to keep the blade moving without force. It is also very important that each shallow cut runs the full length of the foam. Continue to make these long, shallow strokes along your straight-edge, cutting more deeply each pass through. Do this until you’ve fully sliced your way through the sheet.
One of the most commonly used closed-cell foams, polyethylene has a broad range of densities that affects the cell size, firmness, and flexibility of the material. In its lowest densities, it has an inconsistent, bubbly cell structure, which can affect how clean a cutting edge is. Because of this, we suggest not using scissors when cutting polyethylene. Follow the steps for single-pass cutting on sheets thicker than 1/2″ and for thicker pieces of polyethylene foam, use the multi-cut method.