Armor is a plating applied to hulls to increase their armor points in exchange for increasing weight. Armor can be researched in the Naval Lab, with each category of armor gaining a greater base weight and a higher points to weight ratio.
The first category of armor, iron is relatively heavy for the protection it provides. Iron is the first category of armor unlocked in Battle Pirates, and is described as "a light-weight metal", and it is added that it "protects against artillery blasts".
The third category of armor, titanium is lighter than its predecessor steel, but heavier than its successor, depleted uranium. It is added that "titanium's corrosion resistance makes it an ideal material for hull armor".
The fourth and final category of armor, depleted uranium has the highest ratio of armor points to weight. Depleted uranium is described as "semi-radioactive and heavy", and is "the ultimate armor for your ship".