Hades' Robes are the robes worn by Hades, the Greek god of the dead and the lord of the Underworld. People who have committed grave and/or numerous evil deeds in their lives will be forever woven into them. Their faces appear to be in eternal torment. The robe itself is black, but it seems to shimmer with glimpses of the tortured faces.
Percy wins a battle against Hades' undead skeleton soldiers, knocking the death god out of his chariot. Percy grabs Hades by his deathly robes, and Hades teleports out of them, leaving them behind. Percy then threw them in the River Styx to release the unfortunate souls woven into it.