Lots of Red Herring Doctors. Good Grid.

Some good red herrings, but I'm fairly certain if you leave it long enough a sponge will sink.

If I ever see Nigel Farage swimming in deep water, Dobby, I will test that out.

I'd be very interested in your findings BinDipper. Video evidence much appreciated.

good grid, but wouldn't let me have "reversible" for the reversible group, and the water/oil thing is obscure, I'm sure there are other things they have in common - they can all be used to make bottle tops for instance, and I daresay they all contain carbon

I recently did a "things that float" day with some small kids. Sponge lasted all of a few seconds before sinking. Just sayin'. The oil thing, as with all unnecessary extensions into obscurity, is just silly! (Thanks for the interesting fact, though). I'd call plastic and paper materials, not objects!
I've never tried to float a Farage.