But really, what is SR?

[calam]

A thought I had from a thread asking what SR stood for: what is the in universe explanation for how spell resistance works? Does any of the core or setting books have a detailed explanation for how spell resistance works?

[Esprit15]

I always thought it was that saves are your ability to shrug off an effect by dodging, mental strength, or sheer toughness, while SR is the fact that some creatures are not affected by any magic, but only that of people of a certain level of power. “No ordinary mage can harm a [thing].” A spell having SR then comes from whether its effect is actually magic, or if it is a mundane effect that is summoned by magic.

[Keltest]

Spell Resistance is generally either the manifestation of counter-magic of some kind in an innately magical being (I believe this is the fluff used for Drow, for example) or some flavor of null-magic the being in question manifests.

[Buufreak]

I always thought it was that saves are your ability to shrug off an effect by dodging, mental strength, or sheer toughness, while SR is the fact that some creatures are not affected by any magic, but only that of people of a certain level of power. “No ordinary mage can harm a [thing].” A spell having SR then comes from whether its effect is actually magic, or if it is a mundane effect that is summoned by magic.

Considering creatures that have spell immunity are treated as having SR:yes, I'd say this is about the right answer. Thusly, any spell or item that provides SR would somehow apply something akin to a coating that has the same effect, similar to galvanizing steel.

[ayvango]

while SR is the fact that some creatures are not affected by any magic, but only that of people of a certain level of power.
Not all magic but spells. Antimagic field disrupts spells and SU alike. So SU is considered magic too. But SR protects only from spells and spell-likes. So something should work internally like as spell to make SR protect against its EFFECT. And it discriminates effects too: there are plenty of SR:no spells.

[Mr Adventurer]

I think of it as either magical beings who have transcended mortal understanding of typical magic (e.g. fey, dragons) or creatures that are sideways on to normal reality and so get more of a say in how it affects them (e.g. outsiders).