Heads can be "built up" from a number of different materials. This page includes notes on using wire, plastic canvas, and fiberglass. (Slush-cast latex is included under the Latex and Makeup section.) Obviously, this page cannot cover all of the possibilities for head construction; indeed, new techniques are continually being discovered!
For most of these head designs, a harness is needed so that the frame is comfortable mounted on the wearer's head. Inexpensive bike helmets and safety helmets (or just the plastic headband innards) are often adapted for this purpose. I had good luck using a baseball cap, though, so any comfortable headgear of choice can probably be utilized.
Wire Frame Heads
A wire frame understructure I created for a lion head.
Heads can be created by bending and soldering wires to create a framework that is similar to a birdcage. A layer of batting or other interim material is added to create a smooth surface for the application of the fur (on the Widge fursuit, I used plastic canvas for this). Because the wire can be precisely shaped around the head (without the concerns of structural strength in foam heads), this technique is useful for "tight" costume heads. Additionally, the wire strutcture makes for easy mounting of internal components, such as electronics, fans, or batteries.
This technique does have some downsides. It is quite time-consuming to shape and interconnect the wires. And too much metal can create quite a heavy head. On the other paw, these heads are quite durable without the pliability of foam.
Plastic Canvas Heads
Lightweight plastic head created by/for Torrle the wolf.
"Plastic canvas" is a sewing material used for cross-stitching (as I recall). It resembles a thin plastic lattice; you can often purchase it in fabric stores in sheets about one foot by two feet. The sheets are then patterned and assembled, taking advantage of their inherent flexibility to create curved surfaces. Hot glue can be used to join plastic canvas pieces, but you must be very careful as the glue gun is also hot enough to melt the plastic! I have had good results with epoxy (although you need some way to hold the pieces during drying). A number of people have reported a lot of success in simply sewing the pieces together using heavy-duty (upholstery) thread.
A plastic canvas shell is probably the lightest method of head construction; if that doesn't seem important to you now, wait until you've been wearing the costume head for an hour! Heads made this way are fairly durable, although there is no solid structural strength to prevent crushing damage.
