Foam (Types and Tools)?

submitted by Shawn Caldwell "Scully1953"
What is closed-cell and open-cell styrofoam?
The main difference between the two types of foam are the density of the material itself. An closed-cell foam is the type of foam you might find used in packaging electrical or fragile parts. It is a "solid" foam material that is normally molded into a shape that forms around the object it is used to protect. It is different than open-cell foam in that it is a solid foam material. Open-cell foam on the other hand is less dense and has a spongelike appearance. The cells that are referred to in both are actually small holes or air pockets. They are both relatively light materials and can both be used in dioramas, either as a base or used to support your design. They can be cut with a large serrated blade but the best method is to use a hot knife.
What is a hot knife?
A hot knife is a tool used expressly for the cutting and carving of foam. Both closed and open cell foam can be cut or carved using this tool. It is usually a handheld tool with two posts that have a nichrome or very thin wire that is attached at both posts. These posts act as poles that conduct electricity through them. The electricity runs through the wire from the two poles which complete a circuit, the wire heats up as the current flows through it and cuts through the foam like a hot knife through butter, hense the name. The handle of these knives has a power cord that runs to a transformer that regulates the current to the poles and plugs into any household outlet. There are a variety of these tools available, one and I think the most popular looks like a slingshot and has a wire strtched across the two posts. It can be tightened with a set screw to either hold the wire taught to use in cutting straight cuts or can be loosened and used as a loop to cut and carve the foam to achieve gullys or divits to replicate rocky crags, etc. The other types work on the same principle but have a smaller opening between the wires and can be used to trim the foam. There is also a tool also called a hot knife which is actually a rod that heats up and this can be used to carve smaller more detailed etchings in the foam material. It has the appearance of a small rod attached to a handle. There are other foam cutting tools that are very similar to a wood burning tool or a soldering iron that can be adapted to cut foam by utilizing a knife blade tip that attaches like an x-acto knife. The tip loosens and the blade can be inserted and tightened by use of a chuck or set screw.
BE ADVISED that all of these foams, when cut with a heat source will give off fumes that are TOXIC and DANGEROUS to breath in. These tools should be used in well ventilated areas or better yet outdoors if possible.