Rubbery is exactly how I would describe it! So it is a sponge? It encrusts but overall "colony" is shaped like a pagoda cup or a monti cap. It is pretty hardy but in the year or so we've had it, we haven't seen it grow that much if any. First quick glance makes one think of a sponge but closer look, it lacks those porous "pockets" often seen on sponges. Also, when we tried propagating a small piece w/ surgical scissors, it felt very "fleshy" and rubbery.