Outer plasmic shell

The outer plasmic shell, which has dimensionally transcendental properties, alters as the exteior of the TARDIS changes shape. (DW: Logopolis)

With models such as the Type 40 TARDIS, the outer plasmic shell responded to a chameleon circuit.


 * Later, more sentient TARDIS'es might decide what to change into all by it-, him-, or herself.