This article is a brief explanation on how body armor works. It is intended for writers that want to develop a real-world setting.
Batman, clad in the latest Kevlar full body armor, drops in from the open skylight on the ceiling. After he silently incapacitates two security guards, a roving guard spots him and fires his Glock 17 (9mm) pistol. Batman uses his cape to wrap around himself and the bullets fail to penetrate. Unseen by Batman, a sniper with a Dragunov rifle (7.62x54R) fires at the Cape Crusader’s head. Batman shields himself with the cape but the bullet punches through the cape, the cowl, the skull, and out the other side. Batman is now dead.
What is Kevlar?
Kevlar, yes, it is spelled with a capital K, is the proprietary ballistic nylon developed by DuPont that provides some bullet resistance. There are other materials out there but Kevlar is the most well-known.
So how is body armor actually measured?
The Unites States National Institute of Justice (NIJ) is the authority on testing body armor for law enforcement and other non-military uses. The military has its own standards but generally can be compared to the NIJ standards. There are several levels of protection based on the caliber and velocity of the bullet, but for simplicity, I am going to focus on Level III-A, Level III, and Level IV.
Level III-A is the highest rating for soft body armor like Kevlar. It is designed to stop the most common types of threats a law enforcement officer will face on the street (i.e. 9mm, .45ACP, 12 gauge 00 buckshot, etc.). Kevlar will NOT stop carbine rifle calibers (5.45×39, 5.56mm NATO, 7.62×39, etc.). It will also NOT stop battle rifle calibers (7.62×51 NATO, 7.62x54R, .30-06, etc.) Many hunting rifles (.308, .30-30, .270, .223 etc.) are similar to the battle rifle and carbines.
What does this mean for heroes wearing body armor?
Batman’s armor might prevent a thug with a Uzi (9mm) or 1911 (.45 ACP) from filling him full of holes, but when he faces a shooter with a M-16 (5.56mm), AR-15 (5.56mm), AK-47 (7.62×39), or AK-74 (5.45×39), his soft body armor will not help. Soft armor deforms and has another danger, the energy of the bullet can still cause blunt force trauma to the wearer including broken ribs.
What does it take for a superhero, soldier, or police officer to survive a rifle round?
Don’t get shot. But if that cannot be avoided, this is where Level III and IV come in. The primary difference is the ability to stop an armor-piercing (AP) bullet. The official definition of an AP bullet is somewhat ambiguous, but generally, the bullet has a steel or tungsten core encased in lead and wrapped with a copper jacket.
Level III is hard armor, meaning it is constructed from a very rigid material, either ceramic plates or ballistic steel (AR500). This type of armor will stop the vast majority of rifles, pistols, and shotguns used by criminals, law enforcement, or the military.
Level IV armor is also hard armor and designed to prevent penetration even from AP rounds, however, multiple strikes at the same location will eventually penetrate. No armor is 100% bulletproof. Level IV personal armor will be thicker and heavier ceramic plates than Level III. Ballistic steel will be too heavy to wear at this level.
So what is the difference between ballistic steel armor and ceramic plates?
Ballistic steel armor is generally cheaper and nearly indestructible. Ceramic plates are lighter than steel plates but more expensive and can crack if poorly maintained or dropped. It can also degrade over time. If your character is a low-tech vigilante (i.e. Punisher) that cannot resupply after every gun battle, he or she would likely wear ballistic steel armor. For the military, high-priced mercenaries, and law enforcement, they are more likely to wear ceramic plates.
Ballistic steel plates have an issue called spalling, the fragmenting of the bullet when it shatters against the plate. This is addressed by applying a coating, similar to truck bed liner, on the plates. Ceramic plates capture the bullet fragments.
I hope this explanation will help writers that are looking for a real-world description of body armor and the protection they actually provide.