prison clay Share definition Flag A type of clay made in prison, due to a lack of real clay. Consists of 40 percent feces, 30 percent bread, 30 percent paper. Man, there is nothing to do in jail, good thing I made some prison clay! prison clay by Kory Krasowski October 26, 2011 0 0 Get merch Get the prison clay mug. Buy Now — $32.95 See more merch