DR is how much incoming physical damage is blocked by armor. After a successful hit
and any saving throw, subtract DR from the damage.

A natural 20 on an attack ignores DR.

DR (Damage Reduction): DR reduces all Physical damage types: Bludgeoning, Piercing,
Slashing, Fire, Cold, Lightning, Thunder, Acid, Force, Radiant, and Necrotic. DR does NOT
reduce Psychic, Poison, Disease, or Suffocation damage.

Rolling a natural 20 during an attack ignores DR damage reduction value.

Example: You roll 1d6 for damage and get 5. The target’s chainmail has DR 3, so you deal 2
HP damage.