Inured to Energy

(Savage Species, page 36, DnD 3.0)

[General]

You can resist energy attacks more efficiently than normal.

Prerequisite

Resistance to the energy type you specify when taking the feat

Benefit

Your existing resistance to one type of energy increases by 10. You can use this feat only to enhance existing resistances, not to gain resistance to a new type of energy. For example, a demon can increase its resistance to acid, cold, or fire, but it cannot gain sonic resistance with this feat.

Special

You can gain this feat multiple times. Its effects stack. Each time you take the feat, you can either apply it to another type of energy to which you already have resistance, or increase an existing resistance.