Last Updated 5/29/2020, though these mechanics and values rarely change.
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Updated for Patch .12.6
Armor Protection Basics:
Armor in EFT works by stopping bullets completely, preventing almost all damage to the body part it protects unless the bullet penetrates the armor. The processes and math involved are complex with a lot of different factors, but I will break down the process and give rough estimates of what you can expect from some of the more complicated parts.
When your body is hit, if that body part that was hit (or head zone) has body armor or a helmet protecting it, the game checks to see if the bullet penetrates or doesn’t.
The penetration chance of a bullet hitting armor is calculated based on the armor’s level, the armor’s remaining durability %, and the ammo’s penetration value. The chance is then rolled to determine whether or not the bullet penetrates.
If the bullet penetrates, it deals between 0% and 40% less damage based on an algorithm that uses the bullet’s pen value and the armor’s class and durability %. There is a strong correlation between the penetration chance the penetrating round had, and the damage reduction applied to it: The higher the chance the less damage reduction, with high armor classes and high pen values of ammo having lower reductions than others. Most penetrations will be around 20% damage reduction when a bullet starts to penetrate an armor, but things like a PACA vs m995 will result in 0% reduction.
If the bullet does not penetrate, “blunt damage” is applied, which lets through a % of the base damage of the bullet to the body part hit. This % is based on the specific armor’s “blunt throughput” stat, the pen value of the ammo, and the armor’s class and remaining durability %. Blunt damage is extremely low and not a notable factor in kill speed against anything other than level 2 body armors.
Durability of armor is important, the lower the current % of durability remaining the less protection the armor offers overall. The durability % is calculated by dividing the current durability of the armor by the original maximum durability of the armor. Meaning a 60/60 armor is calculated as 60/80, or 75%.
The durability damage taken from bullets is based on the penetration value of the ammo and the armor level of the armor, multiplied by the ammo’s armor damage % and the armor material’s destructibility %. The minimum durability damage armor can take from a single hit is 1, including from individual buckshot pellets. Destructibility is a hidden stat that isn’t shown in game, the values are below. A penetrating round does a little bit less durability damage to armor than a round that does not penetrate. It varies, but is usually around 10-15% less.
“Combined Materials” 0.5
If you want to find the effective durability of different armor to compare how durable different armors are, use the following formula: EffectiveDurability = Durability/Destructibility
—-Hitboxes & Armor Protection—-
Hitboxes are always the same, whether you’re clad in armor or completely naked, they never change in size or shape. Armor simply provides it’s protection to specific hitboxes and head “zones”, and when those hitboxes are struck by a bullet the armor protects them. So no matter what armor you’re wearing they always provide the same area of protection to whatever body parts they say they protect on their inspection screen. So don’t be fooled by what an armor looks like, check the protection zones to see what it actually protects.
—-Head “Zones” and the head hitbox—-
The head hitbox is split into 5 protection zones, each correlating with an angle of impact. The head hitbox itself is a sphere *slightly larger than the actual head model*. The “Top” zone angles create an area of protection in a circle around the top part of the head, starting at a few inches above the temples of the face and going all the way around. The “Eyes” covers the front 120 degrees horizontally and 30 degrees vertically, creating a small slit from the end of the “Top” zone down to about the tip of the nose. The “Jaws” is also the front 120 degrees horizontally, and vertically starting from the bottom of the “Eyes” zone down to about the bottom of the neck, when facing forward. When tilted up, there may be a small sliver of unzoned head, which is always unprotected. The “Ears” cover a 60 degree horizontal angle on both sides of the head between the “Nape” and the “Eyes” zone, going down to about the start of the neck on the head model. Below that is unzoned head and is always unprotected. It’s important to note that both the “Ears” zone and the unzoned head below it is visible from the front due to the cylindrical shape of the hitbox and the front zones’ angles only being 120 degrees wide. You can hit these by aiming for the very sides of the head when faced forward, even shooting past the actual model will hit the hitbox because it is larger than the head model. Finally, the “Nape” continues the last 120 degrees horizontally between the two “Ears” zones and goes from the bottom of the “Top” zone down to the same location the “Ears” end, leaving some unprotected head at the bottom of the neck. In all, when wearing a helmet that covers all 5 zones, there is full coverage across most of your head except for the unzoned small slivers of neck below the “Ears” and “Nape”, and a tiny sliver of neck in the front when the head is tilted back.
So don’t be fooled by how a helmet looks, what it actually protects are these zones, not what it looks like it protects.
—-Angles and Ricochets—-
The angle of impact has no effect on armor except for helmets, which bullets can ricochet off of. If a bullet strikes a helmet within a certain range of angles, the round has a chance to ricochet determined by how shallow the angle is as well as the ricochet chance of both the ammo and the helmet. The required angles and the ricochet chance is determined by the helmet and is different for each individual helmet. If a ricochet occurs it is the same as the helmet stopping the penetration as far as the penetration calculation is concerned, and blunt damage and durability damage continue as they would normally, however the health and durability damage is significantly lowered to the point that there is almost no blunt damage received and the helmet almost always takes the minimum durability damage, which is 1.
Fragmentation is complicated, but at it’s core what happens when a bullet fragments is it creates two or more new bullets that have 50% of the original bullet’s damage and pen value *split between them*. So two fragments of a bullet with 100 damage and pen value would each have 25 damage and pen value, but 4 created from the same bullet would have 12.5 damage and pen value. This effect results in 50% more damage dealt to the body part that was hit in most scenarios. Rarely the fragments can penetrate the body part and hit another body part due to the fragments’ change in direction that normally wouldn’t be hit, causing damage to nearby body parts. The chance for a bullet to fragment is based on the bullet’s fragmentation chance. Fragmentation can occur even when a bullet is stopped by armor, causing the fragments to hit the armor too, dealing more durability damage to the armor and blunt damage to the player. There is a serious bug however, where bullets under a certain threshold of pen value cannot fragment at all when hitting players, and the actual fragmentation chance is lower than bullets’ stat implies due to implementation. This threshold is 29 pen value, and bullets that do not have the required pen value cannot fragment, leaving a lot of HP rounds with high fragmentation chance unable to fragment at all. Other rounds may have significantly lower chances to fragment, based on another ammo stat called “Penetration Chance”, which affects the bullet’s ability to penetrate through objects (not armor).