Different types of armor tend to hold up better against different attacks. As an optional rule, use the following to alter damage based on the armor your character is wearing and the damage type. This would be in addition to Armor Class, not instead of. The damage reduction applied from this variant cannot reduce damage beyond a minimum of 1 damage. This reduction is negated if the creature has resistance to the damage type in question. For instance, a raging barbarian would have resistance to all nonmagic damage, which would overwrite their Hide Armor's reduction to bludgeoning damage.

This variant is more balanced for mid-level adventurers where this slight damage reduction would still matter (unlike in the 15-20 level range) but wouldn't be overpowered (like in the 1-5 range). This variant does require a tad of bookkeeping but since players don't change armor that often.

Remember that these resistances would apply to enemies' armor as well. Apply to creatures that don't wear armor by putting their natural armor into a category. For instance, a dinosaur or dragon might consider their scales to be Plate armor, while a Giant Toad might be considered Leather.

I paired Studded Leather and Ring Mail in with Leather and Chain Mail for those that still think they are worth including.

Padded: Bludgeoning damage and non-heavy piercing damage are reduced by 1.

Padded armor could consist of 20 to 30 layers of cloth that can help absorb impacts from arrows and bludgeoning damage, but not against heavy spears and the like.

Leather/Studded Leather: Slashing and bludgeoning damage is reduced by 1.

The padding helps resist bludgeoning blows while the hardened leather absorbs some slashing damage like a weak short of  cutting mat.

Hide: Bludgeoning damage is reduced by 2.

Hide is thick and usually padded with several layers against hard blows.

Chain Shirt: Non-heavy slashing and piercing damage is reduced by 1.

A simple chain shirt could blunt slashing damage and the flexibility of the chain could disperse piercing blows, but not against heavy weapons with lots of weight behind them.

Scale Mail: Slashing damage is reduced by 1.

The scales of this armor are effective at deflecting slashing weapons away from the body.

Breastplate: Slashing and bludgeoning damage from non-finesse weapons is reduced by 1

Breastplate prioritizes the defense of the torso and sometimes the neck for improved mobility, but leaves the outer limbs exposed for those quick enough to punish them.

Half Plate: Slashing and bludgeoning damage from non-finesse weapons is reduced by 2.

Half plate by definition didn't cover the legs for improved mobility, so someone able to easily aim for that area would deal more damage.

Chain Mail/Ring Mail: Slashing and piercing damage is reduced by 1.

Chain mail could blunt slashing damage and the flexibility of the chain could disperse piercing blows.

Splint: Slashing damage is reduced by 2.

Splint mail can ward off slashes but has gaps between the splints where there is only fabric that piercing weapons would be drawn to as they skid around the metal. Bludgeoning could harmfully bend the splints, which were mostly used on arms and legs.

Plate: Slashing and bludgeoning damage is reduced by 2.

Plate armor is excellent at defending against most melee damage, but piercing damage concentrates each hit on one point and is able to pierce the armor.

New Armor Items

Brigandine: 2000 gp, 60 lbs. This suit of armor is as effective as Splint Mail and is Heavy Armor. It is made from steel plates sewn between elaborate patterned cloth. It is mainly meant as ornamentation for nobility rather than combat. Because of this, the wearer gains advantage on CHA skill checks to either seem like nobility or to persuade or intimidate as if a noble.

Lamellar: 200 gp, 30 lbs. Lamellar is a set of metal plates strung together and worn over your regular armor. It applies a +1 bonus to AC but imposes disadvantage on all DEX-based skill checks and saving throws. You must be proficient in medium armor to wear lamellar effectively.

Padded Jack: 5 gp, 10 lbs. A coat of cloth padding that can be worn over your regular armor. It applies disadvantage to all DEX-based skill checks and saving throws, but it reduces all incoming bludgeoning and slashing damage by 1. You must be proficient in light armor to wear a padded jack effectively.

Reinforced Trapper: 45 gp, AC 15 (disadvantage on stealth). Plates of iron used to reinforce a large chain shirt. You must be proficient in heavy armor to wear a reinforced trapper effectively.

Unique/Magical Armor

Coral Armor: Uncommon. Breastplate, Half Plate, Splint, or Full Plate armor can be made with enchanted coral. Armor of this type become virtually weightless in water, granting advantage on Athletics skill checks to swim in water.

Devilhusk: Rare. A set of +1 Leather, Studded Leather, or Hide armor that is made from a barbed devil's hide. Creatures grappling someone wearing Devilhusk take 1d10 piercing damage at the start of each of their turns. The wearer also has resistance to fire damage. The wearer's AC is considered to be 10+DEX when attacked with a silvered weapon.

Electrified Armor: Rare. Any metal armor can be made into electrified armor. This armor has been enchanted to rebuke attackers with electricity. Whenever the wearer is hit by an attack from a weapon composed mostly of metal, the attacker must make a DC 13 DEX saving throw or take 2d6 lightning damage.

Ghasthide Armor: Uncommon. Leather, Studded Leather or Hide armor can be made with the flesh of a ghast. Such armor can be used once per short rest to exude an awful stench using the wearer's action. Each creature in a 20 ft. radius must make a DC 14 CON save or become poisoned for 1 minute. The wearer also gains advantage on saving throws against paralysis.

Phasing Armor: Very Rare. A set of +1 Leather or Studded Leather armor that seems to be made of a teal mist that isn't entirely too keen on staying in the shape of armor. The wearer can enter the Ethereal Plane for 1 minute a number of times each day equal to their CHA modifier. The creature can move through solid objects but if they end their turn inside of an object they take 1d10 force damage. When they return to the Material Plane, if they are inside of an object, they are transported to the nearest unoccupied space and take 1d10 force damage.

Rhinohide: Rare. Heavy armor, AC 17 (No Dex) (disadvantage on stealth) STR 16 required to wear. Whenever the wearer of a set Rhinohide Armor moves more than 20 ft. in a straight line towards an enemy, the next attack they make against that creature takes an additional 1d6 bludgeoning damage.

Rune-Circle Armor: Very Rare. A Chain Shirt, Chain Mail, or Ring Mail set of armor can be made as Rune-Circle Armor. Each individual ring is enchanted as tiny a circle of protection. The Rune-Circle armor grants the wearer advantage on saving throws against magic. The wearer also cannot be charmed, frightened, or possessed by fiends, celestials, elementals, fey, aberrations, or undead.

Silenced Armor: Rare. A set of silenced armor grants advantage on Stealth skill checks, even if it would normally impose disadvantage on such checks. Any armor can be enchanted to become Silenced Armor.

Snailshell Carapace: Very Rare. This pearlescent Scale Mail armor is composed of magically treated shell from a Flail Snail and has an affinity for magic energy. Succeeding at a saving throw against a non-cantrip spell causes the wearer to gain 1d6 temporary hit points per level of the spell. The temporary hit points fade after 1 minute.

Stone Armor: Rare. +1 Breastplate, Half Plate, and Full Plate can be made with stone shaped by magic. This armor allows the wearer to cast Meld into Stone once per day. The wearer becomes immune to the petrified condition.

A Note on Studded Leather and Ring Mail Armor

In short, this armor didn't exist. It really only exists as a numeric increment in the game to provide more options for armor.

Adding nonessential studs to leather doesn't enhance its ability to deflect attacks, and instead might even help catch slashing weapons or become studded in the wearer's skin from a bludgeoning weapon. Studs only exist for ornamentation and historically only had the function of holding leather armor pieces together.

Ring mail is extremely rare in history and many historians believe it was either used beneath a full set of armor or is simply a misinterpretation of chain mail. In theory, it only seems only effective at deflecting slashing and bludgeoning attacks as it is literally a bunch of giant rings that don't interlock, leaving plenty of room to guide an arrow or pike right on through. It certainly doesn't earn the right to exist as a heavy armor in D&D.