By last count, the Justice Department estimates about 80,000 U.S. inmates live in some kind of restricted housing.
That means being confined to a cell for about 22 hours a day.
"You are going to eat, sleep and defecate in a small room that's actually smaller than the size of your average parking space," said Amy Fettig, a lawyer who runs the Stop Solitary campaign for the American Civil Liberties Union. "And you're going to do that for months, years and sometimes even decades on end."
Fettig said solitary confinement is brutal and expensive.