Definitely ticking the 'other collectables' Tag, these are a fun novelty which seem to have been with us forever, or at least the mid-1970's, when I got my first, but, being a magpie, I now have four! Fake sponge bricks!
My original Christmas stocking brick, one of the 'practical' gifts which were always included; novelty soap, toothbrushes, combs, wiggly straws, things which, however-much fun they were, were also meant to be used daily! It's a soft bath-sponge material.
This was my second, it's a harsher foamed polyethylene, still a batheable foam, but more like garden-game balls, or pet-toys, and was given away at corporate newspaper events, or even with a daily-paper? I can't remember the promotion now, but I dare say, given it's The Sun, that they were for throwing at 'Lefty' politicians, or foreigners?
Once I had two, the track was inevitable, and over a few years I picked up two of these, more modern brick design, and made of recycled foam-rubber granules, much heavier, and not so good for washing!
In the US, they remain a strong, current phenomena, with corporate logo's to the fore, I think they are for throwing at referees' in disgust at their decisions, although I've never seen a clowud of them hitting the pitch, so I guess, once you've paid money for one, your desire to retain your investment in bricks & mortar, mean you hang on to it and just shake it threateningly toward the Man In Black?
There was a trend for mattresses made out of the same heavy, granulated-foam, of my third brick, but often in greys or neutral colours, and they were a favourite of early fly-tipping when they started to break up, and you'd see this stuff in the rubbish pile, odd-shaped lumps, which looked exactly like concrete!
A very commercial one here, from Milton Bradley (MB Games - that's almost like LB for Lik Be!), and hitching a ride on the trend . . . nay, 'craze' for all things Karate, back in the 1970's - "Ah, Soh, Grasshopper!".
Contemporary one, available, new on the Internet as I write, this is expanded-polystyrene, and looks to be pre-coloured, so a few chips or a knocked corner would only add to its aura of realism!
Also current, but a bit naff, and more of a face-cloth? There's a sponge-foam core, but it's covered in a printed-pattern fabric 'pillow', sewn-flush, and over-printed with crude holes, I'd leave this on the self, as the point of the collection is that they look vaguely like bricks, and this doesn't! Although, I guess it does, if you don't display the 'holes'!