How to Cut High-density Foam to Size

Take measurements. The old carpenter's adage "measure twice, cut once" is applicable to working with high-density foam. Before you make a single cut, take careful measurements, write them down, and then take them again. Measure the space or the project where you're going to use the foam. If you're making a bench cushion, for example, measure the bench seat from side to side and front to back, and then measure again to make sure you don't cut the foam too long or too short. In some cases, it's easier to trace the a pattern onto the foam. If you're replacing a chair seat cushion, for example, lay the existing cushion on a piece of paper and trace the edges. You can then cut out the paper and transfer it to the high-density foam.

Mark the measurements on the foam. Using the measurements you took in Step 1, use a marker to mark the points on the foam where you plan to cut. Measure carefully and make a mark, then measure again to make sure you placed the mark at the right point. When you have a series of marks, use a level or straight edge to connect them together, making sure any straight lines are actually straight. If you're tracing a pattern onto the foam, carefully pin the pattern to the foam and trace around the edges, being careful to follow the edge of the pattern closely without moving it.

Cut the foam. Turn on the electric knife to the high setting, and with the blades turned away from you, begin cutting through the edge of the foam along the marks that you made in Step 2. If you're cutting a difficult pattern, circular pattern or more than just a few straight lines, it may be helpful to make a rough cut a few inches away from the edge of the markings, discard the excess foam and then begin careful cutting along the edge of the pattern you marked.