I got two sets of these plates a couple of years ago from a seller in the U.K.
They have a lot of coverage, are completely rigid, almost half an inch thick, and have no backing. They do have a metallic type of ring to them if you knock on them. Any info that was on them has been permanently blacked out. They don't appear to be ceramic, possibly compression molded ballistic fibers of some sort. Does anyone have any info on these?