Expanded aluminum, stainless, copper- the list goes on. If it is a metal sheet, chances are it can be expanded. This process is great, because there is not as much wasted material as there is when perforating metal. With expanded metal, the metal is slit and pulled into to shape (or expanded). Perforated metal is punched or cut out, leaving waste blanks.
It has a fairly clear visual impact, is relatively inexpensive, and is usually very strong for it’s weight. Maybe the visual impact is too strong- conjuring prisions, paddywagons, and industrial storage & machine cages. Available in a wide range of patterns, metals and gauges of metal, it seems like it warrants more use. Tiny expanded silver, someone?
images via Flickr streams and Google images