I didn’t mean this as an additional save to Saves. I meant it as Spell Resistance like Creatures get.
Really, what I envisioned is if someone wears enough Iron in weight they get a Spell Resistance of 1 or 2. Meaning any spell cast at them has to have a Spell Resistance roll (d20 plus the mages Spellcraft) to beat that number. Meaning the spell only fails if a critical fail is rolled. It means one more dice roll, and a very low chance of failure of the mage, but I thought it added more flavor to witch hunters wearing iron.
And Steel is an alloy of iron and carbon, which is why it is not the same as Iron when it comes to magic. So this armor would be like Wrought Iron, so very low carbon.
So this armor if worn would offer good spell protection, but would be softer and more likely to be damaged by steel weapons. And if someone made an easy to damage item as a Legacy item, that seems, scary.