Dimension dam

Dimension dams could be used in dimensional engineering to fit a large room into a tight space. (AUDIO: The Quantum Possibility Engine) TARDISes, which were dimensionally transcendental, made use of them to contain at least some aspects of the interior within the outer plasmic shell.

When a TARDIS was dying, the dimension dams could break down, causing a size leak. (TV: The Name of the Doctor)