The Luna Alloy Mod adds a late-game metal, called the Luna Alloy.
This is, by far, the strongest metal type, and can be used to build near-indestructible walls and furniture. Using it with other mods, such as Embrassures or Save Our Ship 2 Stuffed is recommended to create immensely strong things.
It has also a very high beauty stat.
It cannot be mined, only forged in the Smelter with Plasteel and Uranium.