The armor rule in the 5th edition of D&D is by far my favorite of any edition of D&D. Though there is one system that I can't help but love. The Palladium armor rules grew from house rules of older editions of D&D. I want to do the reverse and see how I would handle a Palladium style system within the frame of D&D 5E.
I want to keep this system very simple so to be upfront about this. I'm going for the feel, while still keeping things simple. I have no interest in realism or direct porting from one system to the next. I'm also doing my best not to throw off the math. It will add more granularity to armor, Which is not everyone's cup of tea. This is totally untested, for now. So here we go.
Armor now has its own hit point pools.
All light armor has a base of 25hp.
All medium armor has a base of 40hp.
All heavy armor has a base of 50hp.
Obviously none standard materials could add or subtract from the base pool of hit points.For example a breast plate made from bone might have only 30hp, While one made from the Dwarven great forge could have 50 or more hit points.
Armor has an AR rating. AR is equal to original AC of the armor plus any Dex bonus it originally had.
Base to AC is now 5 + Dex bonus.
So for example:
Athen the bard has a Dex bonus of +2 and is wearing leather armor. His armor would be:
Leather armor, AC 7, AR 13, 25hp.
Dillan the warrior with a dex bonus of +2 and wearing chain mail would be:
Chainmail, AC 7, AR 16, 50hp
Any roll of the AC or lower is a total miss. A roll greater than AC but less that AR is a hit to the armor, damage is rolled and deducted from the armors HP. Any roll greater than AR is a hit to the character directly and deducts from the characters HP as normal.
Once armor looses its last hit point it is useless and must be repaired or replaced. And the player looses the AR value all together. I'm sure GMs could allow armoring rolls to repair armor allowing armor to regain some or all of its hitpoints back.
This can also add granularity to well crafted items. For example maybe Dwarven armor has more hit points. While Elven steel is so light it adds more to base AC. And Human Fine craft adds to AR bonus.