A hot-wire foam cutter is a tool used to cut polystyrene foam and similar materials.
The device consists of a thin, taut metal wire, often made of nichrome or stainless steel, or a thicker wire preformed into a desired shape, which is heated via electrical resistance to approximately 200°C.
As the wire is passed through the material to be cut, the heat from the wire vaporises the material just in advance of contact.
The depth of the cut is limited only by the wire length. Width of cut is limited by throat, if any.