Is this really a serious reason to buy a laptop, or not, the design? You buy a computer because of its performance, not its appearance- which is something completely subjective in the first place.
I agree about the toughness requirement, but, like others said below the X1 Carbon is called "Carbon" as in "carbon fiber", which it's made of (although the fourth gen model has a lid that's a mix of carbon fiber and plastic).
I've stepped on my second gen. Carbon a good few times and I've dropped my fourth gen on its lid from a coffee table, and they're both hale and hearty.