Armored Casting (3.5e Feat)
From D&D Wiki
Armored Casting [Metamagic]
Whoever takes this feat can ignore arcane spell failure induced by armor to a maximum of 50%.
Prerequisite: Caster level 5th, 18 Charisma
Benefit: You have honed your casting abilities to the point where armor doesn't affect you in the slightest. You ignore arcane spell failure chance up to and including 50%. If you arcane spell failure chance is above 50%, subtract 50% from the total amount. Example: 90% would become 40%.
Normal: You take full arcane spell failure chance when wearing armor.