The Aperture Science Weighted Companion Cube is a piece of testing equipment that is used by Chell in Portal and Portal 2 to climb distances she can't jump and to press buttons. It is a metal box. GLaDOS notes she had "warehouses full of the things" and says the cubes were "garbage" and "absolutely worthless". Where the Aperture Science Weighted Storage Cube has light blue lights, the Comp. C. has pink ones. They look slightly different in the two games and can only be used once in each game.
Chell is said to love "her" Companion Cube, as well as Aperture employee Doug Rattman.