Elemental Resistance is one of three types of resistances in the game, the others being Physical Resistances and Magic Resistance. There are four elemental resistances and, correspondingly, four elemental vulnerabilities

The elemental resistances provide a flat reduction to the elemental damage suffered. The appropriate resistance ability reduces fatigue damage by double these values– like the damage from heat and chill auras. There may be exceptions to this.

The damage reduction takes place after DRN is rolled but before any multipliers are added. This is most commonly the case with Fire spells that often do Fire AP (armor piercing) damage.

• E.g. a unit with 5 FR and 20 prot is hit with 20 Fire + AP damage. First the damage is reduced to 15 because of the Fire Resistance. The unit ends up taking (15 - 20/2 = ) 5 damage.

Someone confirm this calculation

Elemental vulnerablities double the relevant damage received, with the maximum increase being the size of the vulnerability. In the case of poison damage, only the initial poisoning is affected, rather than each subsequent poison tick.

When considering capped damage, vulnerability to the relevant damage type does not increase the damage cap. For example, 1 capped armor negating shock damage can never deal more than 1 damage, even to a unit with shock vulnerability.

Just like MR, Elemental Resistances can be buffed in a number of ways:

• A bless can give access to increased resistances.
• Items can provide elemental resistances. Note that duplicates do not stack, while resistance from different items do stack.
• Certain thrones can provide elemental resistances, such as the Throne of Thorns (+10 PR).
• A number of spells provide elemental resistances. These spells provide either +5 or +10 elemental resistance. Note that spells that provide the same amount of elemental resistance do not stack, but a +10 spell will stack with a +5 spell. I.e. if a commander casts Protection from Lightning and is then buffed with Ground Army they get a total of +15 SR.
• A mage with 3+, 3+, 3+ or 3+ will get a small bonus to elemental resistance against the corresponding element.

When buffing resistances with spells it is important to be aware of the quirks of the Dominions casting AI. Before casting a spell the casting AI will take a unit's current resistance into consideration. If the AI considers the unit's elemental resistance to be high enough it may refuse to cast the resistance buffing spell.

E.g. a commander with high inherent CR (like a Jotun Skratti), a magic item that grants CR (like a Ring of Frost) or CR from a bless might skip casting Protection from Cold or Winter Ward. To avoid this it can be useful to cast battlefield-wide resistance spells or to cast resistance spells before blessing.

fill in all the different spells

fill in all the different spells

¹These are national spells; only LA Pythium has Gift of the Sacred Swamp, while only EA Yomi has End of Weakness.
²Poison Resistance provides +25 PR; it effectively grants both the +10 and the +15 bonuses.