The goo is a completely harmless powder that soaks up 400 times it's own weight in water. When the fun's all done, add the disolver sachet and the goo dissapears.Link (Via Play Library) Alex says:
Gelli Baff is just SPA (sodium polyacrylate). Sounds like they've found a fun way of marketing sodium polyacrylate, a non-toxic, water-absorbing polymer that's used in everything from disposable diapers to agriculture. You can buy a whole pound of it from Steve Spangler's site for $20, as well as SPA in granular form, which can be used as fake snow.
A lot of other substances work well for "busting" the slime once you're done playing, table salt is one, but lots of other household products will do it as well, try some out!
Mark Frauenfelder is the founder of Boing Boing and the editor-in-chief of MAKE and Cool Tools. Twitter: @frauenfelder. His new book is Maker Dad: Lunch Box Guitars, Antigravity Jars, and 22 Other Incredibly Cool Father-Daughter DIY Projects