Not only are the characters named after prisons but they reflect the prisons themselves. Example: Kazan (the mentally challenged character), in Russia is a disorganized prison. Rennes (the "mentor") was a jail that pioneered many of today's prison policies. Quentin (the detective) is known for its brutality. Holloway is a women's prison, and Alderson is a prison where isolation is a common punishment. Leavenworth runs to a rigid set of rules (Leaven's mathematics), and the new prison is corporately owned and built (Worth, hired as an architect).
Director Vincenzo Natali deleted a final moment from the film in which it's shown what is outside the cube. He said when he was paring the film down in the editing room it was the first thing he removed.
All of the characters are named after prisons: Quentin (San Quentin, California), Holloway (England), Kazan (Russia), Rennes (France), Alderson (Alderson, West Virginia), Leaven and Worth (Leavenworth, Kansas).