There are five damage types with Elemental resistances to them: Fire, Shock, Cold, Acid, and Poison.

There are two parts to the damage reduction from an elemental resistance. The first directly deducts damage; the amount deducted is equal to the point value of the resistance, before the Damage roll or the Protection roll. The second reduces the rest of the damage by 2% times the resistance value. So, a unit with 5 Fire Resistance also takes 10% less fire damage beyond that. A unit with 50 points in a certain resistance is thus immune to the damage type the resistance addresses.

Example: An Elite Warrior with Poison Resistance 5 is dealt 15 poison damage. First, the poison damage is reduced by 5, leaving 10 points of damage. Second, those ten points are reduced by 2% * 5, or 10%. 10% of 10 is 1. The Elite Warrior is thus dealt 9 poison damage. It has 13 health. Without the Poison Resistance that hit would’ve been the end for it.

Elemental Vulnerability deducts from Elemental Resistance, and vice-versa.