You can convert any spell into a defense.
Prerequisites: Arcane spellcaster, caster level 10th.
Benefit: As a immediate action, you can sacrifice a prepared spell or unused spell slot of 1st level or higher and gain a Absorb shield of 5 Hit Points / Spell level of the spell or spell slot sacrified. This bonus last for 1 round per Caster level.
Essentia: You increase the Hit Point the Shield can Absorb by +5 per Spell Level / Essentia
Special : The duration also increase depending on the Essentia invested :
(1 Essentia) The Duration become 1 minute / Caster Level
(3 Essentia) The Duration become 10 minute / Caster Level
(5 Essentia) The Duration become 1 hour / Caster Level