Armor vs Weapon Types
This variant rule is designed to simulate how the different types of weapons (slashing, piercing, bludgeoning) interact with the different kinds of armors.
Armor vs Weapon Types
Not all weapons perform the same. If they did, there would be no need for the wide variety of weapons that exist. All weapons fall into one of three categories; Slashing, Piercing, or Bludgeoning. A few weapons, some of them quite exotic, fall into more than one of these categories, and they can be used as either type. Natural weapons are categorized according to their type; claws deal Slashing damage, while powerful fists, slam attacks, and tail attacks deal Bludgeoning damage.
The following table lists the modifiers that are applied to a creature’s Armor Class depending on the armor worn, against the different kinds of weapon attacks. This system is only used for creatures in armor, and the modifiers are not used when attacking unarmored creatures, even if they receive bonuses for deflection or natural armor.

This is a variant rule from 2nd edition AD&D. I believe it adds some realism without complicating things too much; an easy implementation would be for each PC to keep track of his armor in this fashion – Armor Class: ## (Slash: ## Pierce: ## Bludgeon: ## Touch: ## Flat-footed: ##).
A small change « The Dragon’s Lair said,
September 21, 2006 at 9:01 pm
[...] Just fixed a small mistake on the Armor vs Weapon Types house rule. Padded armor had a “-2″ entry on Piercing, which was strange since padded only gives +1 to your armor class to begin with. [...]
shinronin said,
March 3, 2007 at 3:27 am
thanks for the reminder about this great variant. i’d have to dig up my 2nd ed. phb, but wasn’t there also stats on weapon type vs. shields too?
Firkraag said,
March 19, 2007 at 10:52 pm
Yes, but there, all shields were at +1AC – Bucklers were +0 for ranged attacks, and Large Shields were +2 against missiles (or something).