Plasteel

"A combination of steel and acrylic polymers. Plasteel is useful for light defense, but not effective against heavy weapons."

General
Plasteel is the starter ship armor; the level I version is automatically unlocked at the beginning of the game. It is commonly used in beginner-level fleets.

Advantages
Plasteel is very cheap to equip and gives close to no XP, perfect for light ships such as Voyager Corvettes and Harrier Frigates. They are also used on higher-level ships designed for free instant repair (i.e. with a repair time of at most 5 minutes), most commonly the Rancor Battleship and Broadsword Destroyer.

Disadvantages
Plasteel offers little protection but takes up quite a bit of mass. It is immediately replaced by Tritanium, the next tier of armor.

Trivia

 * Plasteel is not a real metal and is thought to be a play on the words "Plastic" and "Steel".