It is just high density commercial grade Melamine foam. http://www.wakeworld.com/MB/Discus/messages/65921/261816.html
Magic Eraser is a cleaning product comprised entirely of Melamine
foam, which, because of its microporous properties, actually removes otherwise "uncleanable" external markings from relatively smooth surfaces. For example, it can remove crayon, magic marker, and grease from painted walls, finished wood, and hub caps.
While this does appear miraculous, it's simply a property of the kind of foam used. The open cell foam is not only microporous, but its substance, melamine, is also extremely hard, which means that it is actually working like sandpaper, but on a very tiny scale, getting into tiny grooves and pits in the subject being cleaned. Because the bubbles interconnect, its structure ends up being more like a maze of fibreglass strands than like the array of separate bubbles in, for example, styrofoam.
The substance simply needs to be wetted to work properly, and it does break down rather rapidly, so that a given block of foam generally is seen to last only a single intensive scrubbing session, though it can be used repeatedly for much smaller marks.
While the name-brand "Magic Eraser" is made by Mr. Clean (Procter & Gamble), the foam itself was already a common product before this new use was discovered, and other companies have also began cutting it up and marketing it for its cleaning properties, either under other names, like Coralite Ultimate Sponge, or as a generic product.
It can be purchased much cheaper through a plastics, upholstry, or industrial supply store. I buy it in 4'x8' sheets for about $40 a sheet.
(Message edited by bocephus on August 03, 2006)