Some materials just don’t want to cut nicely. Foams can create irritating chips that stick to everything, and nylon ropes and polyester fabrics like to fray after cutting. For these materials, you need a hot knife — it can cut through foam, nylon ropes, and poly fabrics easily.
If you’d rather not use a homemade rig made out of wire and a rheostat, Hotwire Direct offers this commercial solution for cutting foam. Their handheld hot knife can reach working heat within five seconds of turning it on. With 16 different temperature settings, you pick the best temperature to slice through foam or to fuse nylon easily, and the circuitry inside prevents the tool from overheating. The blades provided are designed to take the heat without warping over time, but if you want some variety you can add the groove sled to cut different profiles in foam.
Hotwire Direct’s hot knife runs $244, so you if you only need to do a little foam cutting, you may be interested in making your own. If you want to see some of Hotwire Direct’s tools in action, check out this video of hot knife sculpting (.wmv) and this awesome clip of their hot wire CNC machine (Youtube).