The game's armor system is the focus of the latest "ZRPG" design update from DoubleBear Productions' Brian Mitsoda over on the Iron Tower forums. Damage types also get some coverage:
Our armor, much like the weapons, is up to personal preference/need more than it is a linear boost to the defense rating. Armors have a basic defense rating which is subtracted directly from damage. Most sets also have a resistance to certain kinds of attack, which reduces the attack damage by a certain percentage. Resistance bonus is taken off first, and then reduced by the damage resistance of the armor.
For example, if your armor has a defense rating of 5 and reduces Slashing by 10%, then an attack with a knife that causes 10 damage would cause 4 actual points of damage [10 - (10%) = 9 - 5 = 4]. If the 10 points of damage had been from a hammer instead of a knife, the armor's slashing resistance would offer no additional protection and the actual damage would be 5. Damage ratings tend to stay on the lower side, so getting armor with high or more types of resistances should be a priority. There are multiple types of damage in the game:
-Bite Zombie damage.
-Ballistic Gun damage.
-Fire Flame/heat damage.
-Slashing Blade damage.
-Bludgeoning Bashing damage.
-Piercing Spear/Arrow damage.
-Chemical - Gas/chemical based attacks.
As in real life, most armors are designed to protect against a certain kind of attack for example, bullet resistant armor is great for absorbing ballistic damage, but offer little protection against a knife or bite. Matching the armor to the type of opponent you'll be facing is key if your melee guy spend a lot of time fighting zombies, put him in armor with bite resistance. If your ranged girl spends a lot of time exchanging fire with other shooters, put her in ballistic armor. Some armor is general purpose, but doesn't offer the same amount of resistance as specialty armor. Only the highest levels of armor offer adequate resistance to multiple types of attack, but they are difficult to obtain and never offer the level of resistance of the highest level specialty armors.