Exatanium

Exatanium was a metallic alloy used by some species in outer shell of spacecraft.

The claiming to be Steth told Tom Paris a story where he was testing a prototype ship with an extanium fuselage, which he described had "holes in it" after a phaser-fight with the Entabans. He 'limped' back to Benthos where they helped him repair his vessel. 

Exatanium