Armor Plating

Ships can be armored with thicker hull plating and more durable bulkheads and framework. This can only be performed during construction of the ship, and is only available at Clas:1 SCCs. Light armor doubles the cost to HS x 100,000Cr and provides 6 hull points per hull size, medium armor doubles again to 200,000Cr per HS and provides 7 hull points per hull size, and heavy armor doubles once more to 400,000Cr per hull size and provides 8 hull points per hull size.

(source - House Rules Wiki)