Hacker News Reader

Plastics aren't hard, as are ceramics, metals and other cristalling structure, because you can scratch/penetrate it.

Check this out for a quick comparaison about toughness: elongation of polymers is pretty easy. http://images.slideplayer.com/32/9819762/slides/slide_7.jpg

Ugh, sorry, I meant to type "rubber" and typed "plastic" instead. Rubber both resists scratches and permanent deformation, no?

You're asking if rubber is considered hard? What type of rubber do you have in mind?

Any, I guess. Tyre rubber is not easily deformed permanently, although I guess it is easy to scratch.