Polyduranium

Polyduranium was a very rare material.

In 2153, polyduranium was encountered by Enterprise in the doors of the Delphic Expanse sphere and the Osaarian starship's hull. 

Polyduranium was used in a bulkhead on the bridge of the USS Defiant (2370). In 2371, Ornithar expressed an interest in it but he believed it had no real value.