Odds are, you're reading this article right now with your eyeballs, not your fingers. Some people don't have that option, though, which is why the iSense concept, which turns an iPad touchscreen into a literal, touchable screen, is such a great idea.
iSense is a screen protector that you can put over something like an iPad. It's made of a special material that responds to light by forming bumps, allowing the screen underneath to dynamically create physical textures.
This can be used to convert text into braille, or graphics into other feelable shapes, as this handy video shows:
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So what is this magical molecular material? Er, well, it doesn't actually exist. The iSense isn't real, and it's not being developed by Apple. It's just a really, really good idea.