It's been a long time since I used a floppy disk as a coaster, and I'm not sure I could find one now if I needed to. There's something unsettling, though, about these silicone floppy discs [Amazon] intended for use as coasters: they're convincing at a distance, are otherwise just little slabs of silicone, but are more expensive than the complex mechanical media whose superficial appearance they crudely imitate.
Anyway, I ordered a set of 4.