Green Armor

Green Armor absorbs 30% of an attack and provides 100 armor points. While its protection is minimal, it can still save you in a firefight.

Single Player
In Single Player, Green Armor is the most common armor found. While its absorption rate isn't very effective, it's better than nothing.

In Episode 1: Dimension of the Doomed and Episode 2: The Realm of Black Magic, you'll usually find Yellow Armor as much as you'll find Green Armor, so you won't really be using it beyond having some sort of protection until you reach the next Yellow Armor. However, by Episode 3: The Netherworld and Episode 4: The Elder World, Green Armor becomes the most common armor.

Multiplayer
In Multiplayer, Green Armor can be a lifesaver. Absorbing damage, it will prevent you from getting killed by a rocket in one shot, making it very valuable. Try to seek it out if you don't have any armor, because it's much better than nothing.