A Möbius Cube is a device used for transporting sensitive or dangerous objects. It is described as a "carbon-carbon-shell set around a zero impedance containment field folded back on itself." Any object contained within a cube exists within an area of "looped" spacetime, effectively placing it in an area of infinite volume with no walls or borders.
Möbius Cubes often carry nuclear weapons or other dangerous materials. Het Masteen used one to transport an erg to the Time Tombs in hopes of using it to pilot the Shrike's Tree of Thorns.