Chest Armor

The chest is the heaviest slot, and it pays for it. Every heavy breastplate costs 5% of your movement speed, and paired with heavy legs that is a tenth of your walking speed gone.

Protection

Pros

It has the same armour figure as the helmet of its set, so half of a set's protection is decided here: 38 on a Flametal Breastplate, 32 on a Carapace Breastplate and 44 on the Breastplate of the Protector.
It holds the biggest eitr bonuses in the game. The Eitr-weave Robe gives +40%, the Robes of Embla +50% and the Robes of the Caller +60% Eitr regeneration, twice what the matching hood manages.
It is where the damage-type resistances live. The Root Harnesk halves pierce, the Wolf Hide Chestpiece halves frost, and the Flametal Breastplate adds 20% heat resistance for the Ashlands.

Cons

Every heavy chest piece costs 5% movement speed, and the matching greaves cost another 5%. That is the whole 10% a heavy set is known for.
It is the heaviest armour you carry: 15.0 for an Iron Scale Mail against 3.0 for the helmet of the same set.
The Root Harnesk buys its pierce resistance with a 1.5x fire weakness, a bad trade in any biome that burns.
Many of them are Hildir's dresses and tunics, with 1 armour, no upgrade ladder and no effect.

Builds

Go heavy if you block, light if you dodge and robes if you cast. The 5% movement penalty is the price of the top armour figure, and it stacks with the greaves for a full 10%. A light chest piece gives that back and hands you a set bonus instead.

The Fenris Coat is the exception that proves the rule: +3% movement instead of -5%, frost resistance and a set bonus, for 6 less armour than the Wolf Hide Chestpiece from the same biome.

Chest pieces come from Hildir, the Workbench, the Forge, the Black forge, the Frost Foundry and the Galdr table.

Best Chest Armor

Build	Name	Stats
Most armour	Breastplate of the Protector	44 armour at quality 1
Longest lasting	Carapace Breastplate	1800 durability at quality 4
Lightest to carry	Breastplate of Ask	5 weight
Most armour without a forge	Fenris Coat	10 armour at a Workbench

Notes

The movement speed penalties of chest and leg armor add up, so a full heavy set is 10% slower even before a shield is drawn.
Armor reduces physical, fire, frost and lightning damage, but it does nothing against poison or spirit damage.
Every craftable armor piece except Rag Armor gains 2 armor with each upgrade.
Upgrading a piece that is being worn takes it off, so check the gear before heading back out.