Zynthium Plates are the strongest base armor in the game that can be researched, only surpassed by the Capacitive plates blueprint. Players in their mid level stages finish unlocking this armor, and some will use it on their modules to have maximum possible health.
It is advised that Zynthium Plates be used as fast as you can as soon as you finish researching it. However, it also makes repairs increasingly long. However, base repairs cost nothing, so it makes no difference unlike ship repairs, which cost millions of helium-3 if equipped with end game technology.