Armor

Properties
Armor is a property of certain entities is iron marines that makes them resistant to most types of damage. Certain entities have different levels of armor and armor-piercing, which allows them to ignore some (or all) of their target's armor. As a rule of thumb, fire damage and lasers ignore armor altogether.

No armor (0%)
An entity with no armor receives full damage from all sources.

Low armor (1% - 25%)
Makes an entity slightly tougher, but it can be defeated easily as if it had no armor at all.

Examples of entities with low armor: Rangers, Fellplague, Jackbot

Medium armor (26% - 50%)
Makes an entity noticeably tougher against non-piercing attacks. Armor-piercing units such as Snipers, Guardians or Channellers are therefore recommended.

Examples of entities with medium armor: Engineers, Flamewalker, Shellstorm, Grimcrusher

High armor (50%+)
Makes an entity very tough against non-piercing attacks. Armor-piercing units such as Snipers, Guardians or Channellers are almost a necessity.

Examples of entities with high armor: Brawler, Hammergrub, Taskmaster, Geon enforcer (rock mode)