Today I had some students draw all over my classroom walls with markers and when I went to go wipe them with a wet paper towel it just smeared a bit. But when I used a wet magic erasers it came right off. What’s the difference and why does the magic work so well compared to paper towel?
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As other explanations have offered, the physical structure of the melamine sponge is essentially microscopic sandpaper. But there’s a reason that – at the chemical level – using melamine “grit” works much, much better than using sand “grit”. And it relates to the same properties that define/distinguish water, oil, and most liquid cleaners. As I’ll explain below: at the molecular level, **melamine is greasy sandpaper**. That’s the TL;DR.
Most materials (stains, surfaces, solvents, or cleaners) can be characterized by how much they like or dislike water. This spectrum spans from hydrophilic (water loving) to hydrophobic (water fearing), and I will refer to these two extremes as *water-loving* and *greasy* materials in the spirit of ELI5. We all know that oil & water don’t mix, and that you can’t really clean up melted butter or egg yolk using just water. That’s because those greasy things basically ignore water at the molecular level. To clean them, we need soap (a detergent or surfactant), which are substances that – at the molecular level – have *both* properties: a water-loving aspect and a greasy aspect. Adding soap to the mix will allow something greasy to be dissolved in water (and vice versa: something water-loving to be dissolved in oil!). Soap – like many cleaners – is a mediator between the two sides of the solubility spectrum. It helps things dissolve and be removed, often overriding their fundamental chemical properties.
Typically, when we try and clean something, we first make an attempt using some water, then proceed to soapy water (or some other cleaner), and if it *still* isn’t removed, we give up. This is where melamine – and the “magic” comes in: at the molecular level, **melamine is greasy sandpaper**. It will often work on stuff that’s too greasy for water – or even soap – to remove. And the microscopic grit also helps a lot. In contrast, sandpaper (which is not always made of literal sand, I concede) tends to be less greasy than melamine, and therefore it would *not* be great at removing stubborn, greasy stains.
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