Sponge balls are very popular and it is for close up magicians, these balls can also be used for levitation but most of the magicians use them for close up such as party trick etc etc.
One example is when a magician takes two sponge balls and then give one ball to the spectator, and the spectator holds it in to hes hand. Then when the magician takes the other sponge ball and puts it in hes hand it vanish and land on the spectators hand! Sound like a cool trick right? Well watch this short demo video.