Thanks for the info. I totally avoid using them on plexiglass, isinglass, or anywhere other than the gelcoat or stainless. I haven't noticed any scratches on the gelcoat, but will keep it in mind before I lean into a job. What I like best is that they remove stains with relative ease.robertsapp said:Magic Erasers are made of melamine foam and are abrasive. They are basically very fine sanding blocks. They work great in most applications, but you'd probably want to avoid them in situations where you wouldn't want to scratch up the surface. Try one on a piece of Plexi sometime and see what it does to the surface.