Resistance and Vulnerability

Some creatures and objects have Resistance or Vulnerability to certain damage types. If you have Resistance to a damage type, damage of that type is halved against you (round down). If you have Vulnerability to a damage type, damage of that type is doubled against you. For example, if you have Resistance to Cold damage, such damage is halved against you, and if you have Vulnerability to Fire damage, such damage is doubled against you.
No Stacking
Multiple instances of Resistance or Vulnerability that affect the same damage type count as only one instance. For example, if you have Resistance to Necrotic damage as well as Resistance to all damage, Necrotic damage is reduced by half against you.
Order of Application
Modifiers to damage are applied in the following order: adjustments such as bonuses, penalties, or multipliers are applied first; Resistance is applied second; and Vulnerability is applied third.
For example, a creature has Resistance to all damage and Vulnerability to Fire damage, and it's within a magical aura that reduces all damage by 5. If it takes 28 Fire damage, the damage is first reduced by 5 (to 23), then halved for the creature's Resistance (and rounded down to 11), then doubled for its Vulnerability (to 22).