The man hid in the box at the end of a shift of his prison job of making stationery and was carried out by a courier service along with other boxes, reports the BBC.
The escape was "an embarrassing incident" for Beate Peters, the warden of the prison in Willich, in western Germany.
The inmate cut through a tarp in the truck and jumped out shortly after the truck left the prison grounds. The truck driver then noticed the tarp flapping in the wind and reported the cut to the police.
Peters presumes that the man had accomplices outside the prison, and a manhunt is underway throughout western Germany.
Cardboard box expert Solid Snake could not be reached for comment.