Vulnerability

If a creature or an object has vulnerability to a damage type, damage of that type is doubled against it.
Vulnerability is applied after resistance after all other modifiers to damage. For example, a creature has resistance to bludgeoning damage and is hit by an attack that deals 25 bludgeoning damage. The creature is also within a magical aura that reduces all damage by 5. The 25 damage is first reduced by 5 and then halved, so the creature takes 10 damage.
Multiple instances of vulnerability that affect the same damage type count as only one instance. For example, if a creature has vulnerability to fire damage as well as vulnerability to all nonmagical damage, the damage of a nonmagical fire is doubled, not quadrupled.