What does magic resistant armor protect against specifically? All types of elemental magic? Would this then be the best protection against all elements?

If it says "15% Magic Resistance" then it means 15% of the magical spell you are enduring is blocked from damaging you.

Anything that has a magical effect as far as I am aware - so resist magic 15% resists effects of the Thu'um as well as regular spells.

yes and no. While Magic Resistance is against all magic, Elemental Resistances are generally much higher and offer more protection against those specific magic attacks.

One thing Magic Resistance doesn't seem protect from is those magic traps with the soul gem. They seem to be a kind of scripted damage that doesn't check for resistance.

Just breaking this down for the OP.

You can enchant 40% resist elements on 4 separate items, master of enchanting with all relevant perks. (I use a mod which effects enchanting, so that is probably not an accurate number. With the mod I can enchant 46% with perks)

This means that you take 20% damage from one element, and 60% from two. Obviously that would be further reduced with racial bonuses.

Vs. Enchant 25% resist magic on 4 separate items, for 100% resist magic. I think the actual gamemechanic limit is 85%

However with extra effect you gain maximum elemental resistance with 3 items - one item for fire, one for frost and one for lightning.

With extra effect for resist magic, you gain maximum magic resistance with two items only.

So Resist magic is better in the long run, but elemental resistances are better if you don't enchant your own gear.

Qilue: Thanks

Very nice! Thanks to all.

And then there is the breton with the Lord Stone sign. Native 25% magic resistance plus another 25% from the Lord stone and he's 50% magic resistant butt naked. Add to that 15% magic resistance from the Agent of Mara ability and 20% more from the alteration perks and he can have the maximum 85% magic resistance without using any of his available enchantment slots, freeing them up for other effects like magicka regen or reduced casting cost.

General rule of thumb; go for max Magic Resistance first, capped at 85%, then go for Elemental Resists if you can spare the Enchantment slots. A max Magic Resist and a max Fire Resist (also capped at 85%) will together reduce fire damage from spells/dragons by a total of 97%.

This here explains it all. http://www.youtube.com/watch?v=OXyGs_yw3z4

I have a 70% resistance to all magic, combined with an 80% magic absorption rate. It's great to see mages blast me with magic, and not get hurt over half the time, and the rest of the time to see only a miniscule amount of damage done.