asperity

\as-PAIR-uh-tee\, noun:
Roughness of surface; unevenness.

--Compared to the clouds that the Carebears were used to sleeping on, the relative asperity of the Passaic Marriott's cotton bedsheets was literally UNBEARABLE.

--Though undetectable to the untrained eye, Grandpa Wilhelm's back had a subtle asperity to it.