Possibly a synthetic material from which socks may be made. The resultant footwear is on sale in the Store and is sported, albeit in the form of Holy Socks, by Grandson Richard, 39. We know they are Holy because the sight of them, worn by the Grandson, induces Gurder to cut holes in his own socks on the grounds that this is a Sign to all Nomes to do likewise in remembrance of Him.
The Followers of the Sandal in Monty Python and the Holy Grail, who go with one foot bare in homage to the Messiah Brian...
Don't laugh. Officers of traditional Chinese triad societies really wear (or used to wear) only one sandal when in full regalia in memory of the single grass sandal that was a relic of one of the founding fathers of their order. It doesn't help their image as lords of the underworld when they wear grey nylon socks with their single sandal, but if the Hong Kong Police report on triad activities from the 1950s is to be believed, some of them actually did just that!
For those not brought up on traditional British nursery rhymes, I will point out the obvious reference to "Polly, put the kettle on, we'll all have tea".