Working With Foam
It's useful to have several kinds of tools to cut foam. A Foam saw, a band saw, and a foam slicer.
With a Foam Cutter
When using a foam cutter, which has a foot that is about 2 3/4" wide X 6 1/2" long X 7/16" thick, the weight of the foam lays on the f oot and makes it hard to push the cutter through the foam. So it's useful to have several wood slats that are 1/2" (which is really 7/16") X 2 (1 1/2") X 4' or 5' long. Then, when you need to cut foam, put the slats under the foam on both sides of where you will be cutting. The wood slats will hold up the foam and make it easier to push the cutter through the foam.
When cutting the edge of the foam the cutter foot will hold up the edge, thereby causing the edge to be cut slanted instead of straight. To avoid this, put the wood slat under the foam towards the middle about a foot away from the foot of the foam cutter. The wood slat will hold up the middle of the foam up level with the foot of the cutter. This will help you to be able to cut the foam straight along the edge.
Also see the child pages at the bottom of this page