Outer plasmic shell
From Tardis Wiki, the free Doctor Who reference
The outer plasmic shell, which has dimensionally transcendental properties, alters as the exteior of the TARDIS changes shape. The real world interface on the outer plasmic shell enables users to enter or leave the ship. With models such as the Doctor's TARDIS, a Type 40 TARDIS, the outer plasmic shell responded to a chameleon circuit. (DW: Logopolis)
- Later, more sentient TARDIS'es might decide what to change into all by it-, him-, or herself.
