Melamine foam

Melamine foam is a foam-like material consisting of a formaldehyde-melamine-sodium bisulfite copolymer. The foam is manufactured by several manufacturers worldwide, most notably by BASF of Germany under the name Basotect. It has been used for over 20 years as insulation for pipes and ductwork, and has a long history as a soundproofing material for studios, sound stages, auditoriums, and the like. The low smoke and flame properties of melamine foam prevent it from being a fire hazard.
Melamine foam is the active component of a number of abrasive cleaner sponges. It is also used as the main sound and thermal insulation material for bullet trains, due to its high sound absorption, excellent thermal insulation performance and light weight.
As a cleaner.
In the early 21st century it was discovered that melamine foam is an effective abrasive cleaner. The open-cell foam is microporous and its polymeric substance is very hard, so that when used for cleaning it works like extremely fine sandpaper, getting into tiny grooves and pits in the object being cleaned. On a larger scale the material feels soft because the reticulated foam bubbles interconnect. Its structure is a 3D network of very hard strands, when compared to the array of separate bubbles in a material such as styrofoam.
Rubbing with a slightly moistened foam may remove otherwise "uncleanable" external markings from surfaces. For example, melamine foam can remove crayon, marker pen, and grease from painted walls and wood finishings, plastic-adhering paints from treated wooden tables, and adhesive residue and grime from hubcaps. If the surface being cleaned is not sufficiently hard, it may be finely scratched by the melamine material. The foam wears away, rather like a pencil eraser, leaving behind a slight residue which can be rinsed off.