Flak Jacket multiplies all explosive damage taken by 0.75, and caps the maximum damage taken from any one explosive (excluding a direct hit from a rocket launcher or a tank shell) to 75. In effect, this allows the player to survive nearly any explosive attack. Players who find themselves constantly killed by Grenades, Bouncing Betties orM9A1 Bazooka will get much use from this perk. It cancels out and is canceled out by Fireworks. This perk has only a little effect in Hardcore due to decreasing HP of players, since the 75 damage cap is far above the maximum health level. It should be noted that with the inclusion of Flak Jacket, Juggernaut has no effect in reducing damage taken from explosives.

This perk is commonly used in Headquarters and War to prevent being killed by grenades while trying to capture a flag or HQ. It is also especially useful in Search and Destroy, as the enemy will plant Bouncing Betties on the target to kill the player planting the bomb.It can also be helpful when camping the watchtower on Makin because players will often throw grenades into the tower in hopes of killing the player. It is often used with SMGs as they can deal high damage even without perks such as Stopping Power.