Steel
From Tardis Wiki, the free Doctor Who reference
Steel was a type of metal used in construction.
Draconian swords were made from the finest steel in their galaxy. (COMIC: The Warrior's Story)
Steel was a part of the construction of Icarus Falling's bulkheads. (COMIC: Fire and Brimstone)
The hull of the Octopus Rock was made of seven inches of steel. (AUDIO: Submission)
The Cybermen created by John Lumic, the owner of Cybus Industries were constructed of bulletproof steel. (TV: The Age of Steel)
In 1991, three inches of steel lined every wall of the Cabinet Room inside 10 Downing Street. (TV: World War Three)
