Zynthium is the final armor to be researched and unlocked, and the strongest armor that can be researched. They are incredibly prevalent choice of armor being very light and offer significant protection. Players usually begin unlocking Zynthium when they have unlocked Nighthawk frigate.
As Zynthium is the best researchable armor in the game, it is also the most costly to research and repair. They are certainly worth it, on mark V ships, players often fit Zynthium IV/V on their ships. Most players usually equip all their weapon, shield and utility needs and then fill the remaining space with armor.