The Large Armor's looks depends on the game, but in every game it is featured in, it gives the player 100 armor points when picked up. The armor is a blue suit of armor in Serious Sam 1 and Serious Sam: Next Encounter, a suit of yellow armor with a helmet and a shield in Serious Sam 2 and a red suit of armor in Serious Sam Advance and Serious Sam: Double D. Exclusively in Serious Sam 3: BFE, the large armor can exceed the normal armor cap of 100 up to a maximum of 200.
Extra Large Armor is usually given to the player before a large fight occurs, which is a big hint to the player that they're going to be involved in something big. It also appears between waves in certain difficult levels, such as Metropolis. When picked up, it triggers the next wave.
It can also be found in secrets as often as Super Armor.