Damage Reduction

Damage Reduction (DR) represents a flat amount of damage that an item, power, or natural ability can reduce. Typically, damage reduction will apply to a specific damage type (such as Fire, Piercing, or Holy), but can also apply in broader categories, such as Weapon Damage which applies to all weapon damage types (i.e. Bludgeoning, Chopping, Piercing, and Slashing). Sometimes, Reduction is overcome by specific properties (such as Silver Weapons overcoming a Devil's Weapon Reduction), in which case the attack deals full damage.

Damage of Multiple Types

If you are subject to an effect that deals multiple damage types, you must have reduction to both damage types to gain the benefit (if you do have Damage Reduction to both types, the worse of your reductions applies). For example, if you are subject to an attack that deals Fire and Necrotic damage, you must have Damage Reduction to both types to gain any benefit.

Damage Reduction from Multiple Sources

If you gain Damage Reduction from multiple sources, the greater amount of Damage Reduction applies (i.e. they are not cumulative). Which Damage Reduction is best may vary from attack to attack, depending on the type of damage suffered. For example, if you have Damage Reduction 15 to Lightning damage and Damage Reduction 5 to all Damage, the former will apply whenever you suffer Lightning damage, and the latter will apply for all other damage types.

Reduction and Resistance

It is possible for a creature to have both Damage Reduction and Damage Resistance to the same energy type (Damage Resistance indicating a 50% reduction in all damage of the specified type). If this is the case, Damage Reduction is applied first before Damage Resistance. In other words, Damage Reduction is subtracted from the total damage before the damage is reduced by 50%.

A Natural 20 on an attack roll automatically overcomes Damage Reduction, but not Damage Resistance.