Lead

Lead was a metallic element.

Vardans could not broadcast themselves through lead. The Fourth Doctor had his Presidential chamber decorated with lead lining to keep the Vardans from reading his mind. (DW: The Invasion of Time)

Torchwood Three kept a radiation sponge in a lead-lined case. (TWN: Another Life)

On Venus, the Daleks forced Jeff Stone to work at a lead mine. (DAN: Red for Danger)

On Wengrol, Yend scientists built massive lead buildings to protect themselves from Mortain's radiation while they worked to find a cure for the mutations plaguing their world. (DWAN: The Sons of the Crab)