Ultra-Bastard D&D: Armor

Armor Class (AC) is the number that must be hit to successfully land a weapon attack on an enemy. Monster armor class is a target number for ability checks and player AC is a saving throw. When attacking a monster, a player must roll above the enemies AC to hit. When being attacked, a player must roll under their own AC to avoid being hit.

The unarmored default is AC 8.

I do not associate a particular armor class with a particular type of armor. You can have leather or chain armor from +1 though +6.

Type	+ to AC	Description
Light	+1 - 2	+ Dexterity mod in melee
Heavy	+3 - 6	Penalizes stealthiness
Shield	+2	Penalizes stealthiness
Helmet	+1	Penalizes perception

Add or subtract dexterity mod against melee attacks while wearing light armor.

You cannot sneak up on someone while you are in heavy armor or carrying a shield. Heavy armor sounds like a sack of cans and bottles.
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Special Rules: These are all optional.

Encumbrance: Armor consumes a number of inventory slots equal to its AC bonus.

• Specialty, high-quality armor might have lower encumbrance.

Shields shall be splintered: "Any time you take damage, you can opt instead to say your shield absorbed the force of the blow. The shield is shattered and must be discarded, but you don't take any damage from that hit."

Variant shields: 

Type	Examples	Description
Small	Buckler	+1 AC, no stealth penalty
Medium	Parma, heater	+2 AC, stealth penalty
Large	Kite, scotum	+2 AC in melee, +4 vs missile attacks

Scavenger Armor: Separate armor for body zones each adding a small AC bonus:

• Light Armor - Two hit zones: head and body
• Heavy Armor - Three hit zones: head, torso, limbs
• Generally, plate adds +2 to a zone, chain/other adds +1. Torso counts double.
• Examples:
• Chain shirt covers torso and limbs adds +3 AC
• Steel great helm, covers head, adds +2 AC and disadvantage on Alertness checks
• Breast plate, covers body only adds +4 AC