Body armor is a type of item featured in I Am Alive. It provides protection for the Protagonist from two Pistol shots and four Machete strikes before the Protagonist's actual Health is damaged. The armor is damaged if the player falls from a certain height. In terms of appearance, it adds one layer of metal bandaging and padding onto the protagonist's front side.
Body armor is highly common in the final Chapters of the game, found among the larger and stronger members of the Gangs that inhabit Haventon. When confronted with a armored enemy, the player will receive a notice that informs shots to the vulnerable parts of the enemy's body (his head and legs) are prime areas for attacks. Also, the shotgun can penetrate body armor unlike the other weapons.
Picking up multiple body armor does not provide more protection, it just removes the previous armor from the Protagonist. If possible, save the other body armor by leaving it on the ground, and then come back when your current body armor is either gone or heavily damaged.