These boxes contain pieces of very light melamine foam*. (I assume this is the same melamine that the Chinese were using to fool the protein tests for baby formula. This form is way different, however.)
The brand name stuff always seems pretty darned pricey to me, so I gladly nab a box of the house-brand.
Anyway, with a few drops of water these foam blocks will remove finger sludge from your keyboard (yes, your laptop will look “like new”), soap film from your shower glass, marks from painted baseboards, and the like. Without marring the surface. Like magic!
So, if you didn’t know about what a marvelous cleaning helper melamine foam is, now you do!
* Apparently, it’s a formaldehyde-melamine-sodium bisulfite copolymer. Say that three times, fast!