Does Light armor Profiency Negate ASF with mthril Breastplate

[Barbarian Horde]

If it does please explain why.
If it doesn't please explain why.

I don't have an answer and would like details on this.

[Darrin]

No.

Proficiency with armor has nothing to do with ASF. You make an ASF check whenever you are wearing armor and cast an arcane spell, as per the PHB:



Casting an Arcane Spell in Armor: A character who casts an arcane spell while wearing armor must usually make an arcane spell failure roll.


Certain classes, such as the Bard, can cast bard spells while wearing light armor and do not incur ASF. This is part of the bard's class features, and is not because they are proficient with light armor.

A mithral breastplate is considered light armor for the purposes of proficiency. A bard wearing a mithral breastplate does not have to check for ASF because it's considered light armor, and bards can ignore ASF when wearing light armor.

[Âmesang]

Assuming you're a bard, battle sorcerer, or another class that ignores arcane spell failure whilst wearing light armor? If so, I want to say "yes," although I believe in Pathfinder you would still need medium armor proficiency to not suffer the armor check penalty.

Light armor proficiency by itself shouldn't negate the arcane spell failure chance itself (which I believe would be 'round 15%).

[DrMotives]

What armor proficiency does; either light, medium, or heavy, is to make the armor check penalty apply only to certain skill checks instead of all movement actions. So no proficiency = penalty applies to attack rolls, ride checks, and anything else involving more movement than sitting at a desk working. Spell failure has nothing to do with it.

[exelsisxax]

In pathfinder, mithril items don't count as lighter except for encumbrance purposes, so no class ever receives any benefit other than the standard ASF reduction from being made of mithril.

I'm not sure if 3.5 has that exact stipulation per RAW.

[Zanos]

In pathfinder, mithril items don't count as lighter except for encumbrance purposes, so no class ever receives any benefit other than the standard ASF reduction from being made of mithril.

I'm not sure if 3.5 has that exact stipulation per RAW.
Nah, 3.5 mithril counts as lighter for all purposes.

But as others have mentioned, armor proficiency and arcane spell failure aren't tied to eachother. You would need some ability that lets you ignore light armors ASF for this to matter, like being a bard or a warlock.

[Psyren]

In pathfinder, mithril items don't count as lighter except for encumbrance purposes, so no class ever receives any benefit other than the standard ASF reduction from being made of mithril.

This is incorrect - it says they count as lighter for "movement and other limitations." A rogue in a mithral breastplate can still use their evasion ability for example.

[exelsisxax]

This is incorrect - it says they count as lighter for "movement and other limitations." A rogue in a mithral breastplate can still use their evasion ability for example.

Evasion and barbarian fast movement are restricted by encumbrance, mithril states that it does reduce armor category for those purposes.

If "other limitations" meant everything not excluded, any ability requiring heavy armor wouldn't work if it was mithril.

[Psyren]

Evasion and barbarian fast movement are restricted by encumbrance, mithril states that it does reduce armor category for those purposes.

If "other limitations" meant everything not excluded, any ability requiring heavy armor wouldn't work if it was mithril.

Abilities are not limitations. What it means is that it counts as lighter only if not doing so would limit you in some way.

[Barbarian Horde]

Would Mithral make the armor count as light armor? At this point qualifying it for classes stated above?

[Psyren]

Would Mithral make the armor count as light armor? At this point qualifying it for classes stated above?

Yes, it will count as light. The ASF will only be reduced by 10% nominally, but if you have a class feature that says "you get to ignore all ASF in light armor" then that will apply to mithral medium armor (e.g. mithral breastplate) too.

You do however have to still be proficient in medium armor to avoid ACP entirely. If you are not, the ACP will apply, but is reduced by 3 (so mithral breastplate will have ACP of -1 instead of -4.) Note that the Armor Expert trait can be used to reduce this to zero.

[Lord Vukodlak]

Most mithral armors are one category lighter than normal for purposes of movement and other limitations. Heavy armors are treated as medium, and medium armors are treated as light, but light armors are still treated as light. Spell failure chances for armors and shields made from mithral are decreased by 10%, maximum Dexterity bonus is increased by 2, and armor check penalties are lessened by 3 (to a minimum of 0).

Movement is pretty easily defined but how do we define limitations... well the first thing that comes to mind is you can't use X class abilities in heavier then Y armor. Mithral counts as a category lighter for those purposes to a minimum of light. Even the old FAQ advised you'd treat the proficiency required to wear the armor as a category lighter.
'
For me the simplest least rule intensive decision was Heavy armor made of Mithral was medium armor, and medium armor made of mithral was as light armor etc. For class features for proficiency etc etc. If you happened to have a class ability that only worked in heavy armor? oh well don't work in Mithral

But that's 3.5 what about Pathfinder well that question has already been officially answered.


Mithral armor: What exactly does it mean when it says mithral armor is counted as one category lighter for “other limitations?”

This means that mithral armor allows its wearer to use it when her own class features or special abilities demand her to wear lighter armor; in other words, the character wearing the armor is less limited. For example, a bard can cast spells in mithral breastplate without arcane spell failure, a barbarian can use her fast movement in mithral fullplate, a ranger can use his combat style in mithral fullplate, brawlers, swashbucklers, and gunslingers can keep their nimble bonus in mithral breastplate, rogues keep evasion in mithral breastplate, a brawler can flurry in mithral breastplate, characters without Endurance can sleep in mithral breastplate without becoming fatigued, and so on. It does not change the armor’s actual category, which means that you can still store a creature one size category larger in a hosteling mithral fullplate, and you can’t enhance a mithral breastplate with special abilities that require it to be light armor, like brawling (though you could enhance it with special abilities that require it to be medium armor), and so on.
http://paizo.com/paizo/faq/v5748nruor1fm#v5748eaic9t7t

[Psyren]

I had actually forgotten that FAQ, but glad to see that my own interpretation squares with the official one :smallsmile: