Metalert

Metalert was an enhanced form of dalekanium created by Zeg to overcome the problems Daleks would have during space travel. It was stronger and capable of withstanding great heat, acid, and mercury, but was not immune to extreme cold, such as liquid oxygen. Zeg was accidentally coated with metalert. (COMIC: Duel of the Daleks)

Dalek Sec's casing was also made of metalert. (PROSE: Birth of a Legend)

Behind the scenes

 * According to the Doctor Who DVD Files, the Dalek Emperor seen in the television story The Parting of the Ways was reinforced with metalert.
 * James Johnson's "headcanon" for the bronze Dalek Pilot design he rendered for the cover of What Lies Inside? stated that their battle-shell was infused with Black Metalert to withstand excess heat and space fatigue.