polystyrene can be cut several ways but the easiest and neatest way to cut polystyrene is by using a hot wire cutter. polystyrene can be cut with a sharp knife but it often leaves a rough edge, likewise you can saw through it using a hack saw blade but again the finish is far from perfect.
An hot wire cutter is perfect for cutting most types of polystyrene including insulation. The hot wire cutter works by passing current through the taught nichrome wire, which in turn heats up to approximately 200 degrees C. This intense localised heat melts the polystyrene in front of the wire. This makes it possible to carve out some very complicated and detailed shapes in a very fast time.
Here you can see the hot wire cutter in use on some polystyrene insulation. This type of insulation called "Jablite" is a lot harder to cut than standard polystyrene as it contains small particles that are difficult to cut through as they are fire resistant. This particular hot wire cutter runs from a 4.5v Battery. These types of cutter are readily available in model making shops!
Here you can clearly see that the polystyrene has easily been cut into an intricate shape using the hot wire cutter. As the wire burns through the polystyrene it is essential that the hot wire cutter is only used in well ventilated spaces.
The hot wire cutter in conjunction with a square makes easy work of cutting through this polystyrene insulation. Hot wire cutters are available in all shapes and sizes, typically the larger the cutter the thicker the nichrome wire is. Some hot wire cutters can accept pieces of polystyrene that are a few feet in width. .