What would be more valuable in a post-apocalyptic world and/or more suitable to be used as currency: plastic or metal bottlecaps?
The Fallout video game series popularized the use of metal bottlecaps as a form of currency in a post-apocalyptic world as they are, supposedly, difficult to forge. However, wouldn't it be more difficult to assemble the tools for plastic injection moulding than metalsmithing? Thus forging plastic bottlecap currency would be more difficult, not to mention the ubiquity of plastic bottlecaps means they'd be more common (scarcity is probably not something you want for a medium of trade).
On second thought, I considered the fact that the imitation-proof quality of the proposed currency would most likely be pointless as a post-apocalyptic society would probably not use a fiat currency, the value of which is derived from the government, but revert to some form of barter-and-trade where the selection of a common currency of exchange would be more dependent on its inherent value than any government fiat. Would then the currency be metal bottlecaps, which have more utliliarian value since they can be melted down be used for other purposes?