We're all familiar with printed circuit board material, also called PC board, PCB, printed wiring board, or PWB—though those last two names don’t seem to have caught on in the engineer's lexicon, despite prodding by various standards bodies such as IPC (see here) which began in 1957 as the Institute for Printed Circuits but has since changed its name. The most common type is FR-4, with glass-epoxy substrate (see here), but there are other materials available, such as low-cost, easily punchable phenolic as well as sophisticated, RF-optimized types.
You can get FR-4-based PCB material in many sizes and standard types: unclad; copper-clad on one side; clad on both sides; with heavier cladding; and even with a pre-drilled, closely spaced array of holes. It's a strong, stiff, hard-to cut, tool-dulling, and very useful material which engineers use in many product roles besides its primary purpose of provide real estate and interconnect circuits, of course.
For example, it's a quick and effective way to build a shielded box around a sensitive sub-circuit, since you can quickly solder the edges and get very good RFI/EMI attenuation. Or you can use it as an "above the board" third dimension to bring both power and ground (aka signal common) to parts of a circuit which need lower IR drop in a supply rail, or lower ground impedance.
But the real beauty of this PCB material is its many non-circuit uses. I once cut a piece in a large, skinny "U" shape to be an internal stiffener within the floppy leather handle of a well-worn, classic briefcase. Another time, I laminated some to a plastic shelf which had cracked to poor design and material; the hole pattern in the PCB material acted as a "grab zone" for the epoxy adhesive and really made for a solid joining of the two layers.
Among the other interesting uses is as a structural base for hand-building of model railroad turnouts (sometimes but erroneously called "switches"). The board comes etched with a tie pattern, to which the modeler solders the rails; the PCB forms a rigid yet thin base. You can also buy individual model-railroad ties for the same purpose, see here. (Of course, the modeler also has to cut a small gap in the ties using a cutoff wheel, or he'll have the kind of "rail-to-rail" performance which shorts the current-carrying rails. ;-) There are other examples; these are just a few that come to mind.
What have you used PBC material for, besides electronic circuits and functional support? Have you ever used it to do an emergency repair, or as a structural element in a clever project design?
[If you come up "blank" to the above challenge, I'll give you an alternative question: what non-wiring uses have you had for shrink tubing, another wonderful item in the engineering kit? You can consider standard, small-diameter, thin-wall tubing; large -diameter tubing (up to several inches); thick-wall tubing; and even the kind which is lined internally with a thermoplastic adhesive which melts during the "shrink" cycle and so forms a tight, watertight seal.]
I'm always interested in how people adopt and adapt basic items to solve problems for which they weren't originally intended or developed—that's a large part of the creativity and innovation process. ◊