Sponge balls

From MagicHistorian

Spherical Sponge that compresses flat but springs open into view quickly. Commonly availible in red but over the years have been made in a varitey of rainbow colors from black to lime green. The most well known manufacturer of sponge balls is Goshman started by the magician Al Goshman. They come in many sizes from 1 inch to 6-7 inches. One type of sponge used is called "Super Soft". When these sponges get wet they expand about a 1/4 of their size more. (respectively)

Usually they are used in routines where they disappear, re-appear, multiply, and vanish from the magicians hand, pocket, even the spectators hand. There have been variations made where the sponge is cut to resemble bunnies, squares, and pyramids. See: Sponge Bunnies