Exatanium

From Memory Alpha, the free Star Trek reference.

Exatanium is an metallic element used by some species in outer shell of spacecraft.

Steth's ship had 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. (VOY: "Vis à Vis")