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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The ‘active ingredient’ of magic erasers is [Melamine](https://en.wikipedia.org/wiki/Melamine_foam). It is a surprisingly hard material that only feels soft, and when it’s a foam it has many abrasion surfaces to work with. So essentially it is a sandpaper that can get into cracks of anything that is harder than it (and it scratches off layers of anything softer than it). Once it scratches off the thing it’s cleaning, it crumbles away from the sponge while surrounding it; so greasy residues are caught and contained, kind of like a pencil eraser and graphite.
Edit since this got some attention, but I think people are focusing on the wrong part: Most aggressive cleaners are abrasive in some way (they are also known as [scouring powders](https://en.wikipedia.org/wiki/Scouring_powder)), so melamine isn’t special for that; instead, it’s because it’s a “reticulated foam” (that means “net like”; the ‘bubbles’ of the foam are only made out of the lines where they intersect, while there is still lots of open space). Because of this, both the hard melamine can get into the cracks as I mentioned above (the foam is flexible, even though it’s made out of hard stuff) and the mess can actually get into the foam instead of just being pushed away. Once the mess is inside the foam, the chunk of foam with it can break off and keep it from going back and being a mess. This second part is why melamine works in places that chemical cleaners or scouring powders have a tough time.
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A magic eraser is literally just very fine sandpaper, which is why you need to be very careful using them. A paper towel is just fabric.
Magic erasers will 100% take the paint off your walls on top of whatever marker/crayon/scuff you’re trying to get off because you’re essentially sanding your walls. You’re not just trying to soak up the marker with fabric, you are using an abrasive to take material off the walls.
Super elif, magic erasers are made of very tiny things stuck together. When wet they unstick and are like very tiny grains of sand. So basically you’re just using very fine sand paper.
ElI5 : it’s basically a very fine sand paper. You’ll notice on some things it actually removes part of the finish from it.
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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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