Your spells of that element are now even more potent than before.
Prerequisite: Elemental Focus.
Choose an element to which you already have applied the Elemental Focus feat. Add +1 to the Difficulty Class for all saving throws against spells from the element you select, but a -1 to its opposing element. This bonus and penalty stacks with the one from Elemental Focus.
Special: You can gain this feat multiple times. Its effects do not stack. Each time you take this feat, it applies to a new element type to which you have already applied the Elemental Focus feat. This stacks with the Spell Focus feat.