There are several types of hot-wire foam cutters that range widely in their sophistication.
A simple hand-held foam cutter may consist of a tensioned wire attached to a handle. The wire is manually guided through the larger piece of foam to cut out any desired free-form shape. For larger items or for more precise foam cutting, a table foam cutter may be employed. A foam cutter table may consist of either a vertical or a horizontal wire with vise-like guides to hold the foam in place as it's moved.
