• A breastplate is 6 ac, 3 max dex, -4 check penalty
  • If it's Mithril, that makes it 6 ac, 5 max dex, -1 check penalty
  • The Armor Expert trait pushes the check penalty to 0.

Since there is no check penalty you don't even need proficiency to use this because the downside of not being proficient is related to check penalty. Now you can have rogues with good dex going around with 10-12 AC compared to full plate fighter with at best 11 AC with huge check penalties to his skills.

And since its light armor, they don't suffer the move penalty (due to mithril saying the armor counts as a category higher, except for proficiency requirements).

Doesn't this seem really flawed? Thoughts?

  • \$\begingroup\$ Apart from the trait, you can get the same effect for 5000gp using the Comfort enchantment from the Pathfinder Society Field Guide. If your DEX is +5 or less, it is cheaper than a mithral chain shirt of the same AC (starting at +1 for the breastplate). \$\endgroup\$
    – MrLemon
    Commented Jun 3, 2014 at 12:42

7 Answers 7


Various points you seem to missing:

Traits are valuable

You only get two, and some of the options you can get for a trait are fantastically powerful. Reducing ACP by 1 is really minor.

Mithral is expensive

For a medium armor, it costs 4,000 gp; that’s quite a bit. Affordable by mid-low levels, sure, and quite cheap at mid-high levels, but for a while there, if you have mithral, you don’t have any +1-equivalent special properties (+1 something breastplate and mithral breastplate cost the same, after all). By the time you can afford a +1 something mithral breastplate, someone else can just about afford a +1 2-equivalent breastplate, which could be that much better.

Eventually, the fact that mithral is a static cost rather than a quadratic one as with most magic properties makes it a fairly cheap thing to get, but at that point you have to consider...

Making something from mithral means it’s not something else

There are a lot of special materials in Pathfinder; mithral’s a good one, but there are plenty of other good ones. Adamantine armor gives DR/– and is extremely difficult to damage. Dragonhide reduces the costs of adding energy-resisting magic to the armor. And so on.

3.5 let Mithral reduce the proficiency necessary to wear armor; it never broke anything

Rogues, along with bards and rangers, used to be able to wear mithral breastplates with proficiency, because 3.5 did not have Pathfinder’s clause that mithral doesn’t reduce the proficiency required to use the armor. This never broke anything; it was a useful feature but not an amazing one. In this respect, the fact that these classes can wear mithral breastplates with no penalty if they have Armor Expert is a loss for them, because they used to not even need Armor Expert.

You really aren’t getting that much return on your investment here

Attacks can target any of five stats: armored AC, touch AC, Fortitude, Reflex, and Will. This armor is effective only against one of those, and it’s a fairly modest bump in that defense (+2 AC vs. the more typical chain shirt for light-armor-wearing classes).

So you’re talking about 4,000 gp and a trait (and the inability to use a different material) for a modest boost to just one defense of many. That’s not outrageous at all; in fact I feel like that’s a pretty poor trade, overall. Especially when you consider that, on the whole, armored AC tends to be targeted by HP damage; no one wants to get hurt, but you have your HP there as a cushion to absorb a few blows. Meanwhile failing a single Fort or Will save can cripple or kill you, or worse!

  • \$\begingroup\$ I think you are underestimating the +2 AC in terms of cost here. 4150gp for the mithral breastplate is still cheaper than the cost of an enchanted mithral chain shirt of equal AC (5100gp), with increasing price gap for higher enchantments. If you "buy the trait" with the Comfort enchantment instead (with slight added benefits), it breaks even at 7 AC: +1 Comfort Mithral BP is 10150gp, +3 Mithral CS is 10100gp, at 8 AC the Breastplate is 4000gp cheaper (which in fact means that there's no reason to ever wear a +4 mithral chain shirt as far as I can see). \$\endgroup\$
    – MrLemon
    Commented Jun 4, 2014 at 11:41
  • 8
    \$\begingroup\$ @MrLemon You are just overestimating the value of armored AC. Armored AC is not something you should invest that much in. Having a +3 armor is almost always a mistake; you should have +1 armor, with special properties from then on. You’re also making the chain shirt mithral when it doesn’t need to be; most of the effects of mithral are wasted on a chain shirt. \$\endgroup\$
    – KRyan
    Commented Jun 4, 2014 at 12:22

That's certainly a powerful combo, but it's not ridiculous. It gives a similar AC to a character in full plate, and requires a trait, which full plate doesn't. That combo is likely the best armour for a rogue or other light armour user, but that's going to be the case whether they use Armour Expert or not. For an AC-conscious light armour user, a Mithril Breastplate gives them +3 AC (2 armour, 1 dex) and -1 Attack compared to a masterwork Chain Shirt, which is often a good trade off.

With a maxed out Dex, a character in a Mithril Breastplate will have an AC bonus of 11 (6 armour, 5 dex). With a maxed out Dex, a character in Mithril Fullplate will have an AC bonus of 12 (9 armour, 3 dex). The Fullplate user needs to have heavy armour proficiency, spend an extra 5000 gp, and has -10 feet of speed, but doesn't need a trait. That seems perfectly well-balanced to me. The fullplate user will have a -3 ACP, but that's not really awful for heavy armour.

  • \$\begingroup\$ ...and requires a trait, which full plate doesn't Wearing the full plate with no penalty requires an extra Feat (heavy armor), it may be a "free feat" for some, but it's still a feat. There's also a speed cost that you are forgetting to mention. Regardless of proficiency, Full Plate will slow you down significantly. \$\endgroup\$
    – Gates VP
    Commented Jun 10, 2014 at 17:45
  • 2
    \$\begingroup\$ I don't think I've ever seen someone actually take an armour proficiency feat in anything but the most esoteric of builds. It may be a cost, but it's a cost that's so rarely paid that it doesn't really count when talking about the general case. It's very common for a character who wants to use heavy armour to already have proficiency, but it's relatively rare for someone to take that particular trait. \$\endgroup\$
    – DuckTapeAl
    Commented Jun 10, 2014 at 19:19
  • \$\begingroup\$ But it is a cost that's inherent in the class you're taking. If we assume that classes are balanced (for some value of balanced), then taking a class like fighter means that you're getting feats like Heavy Armor and Martial Proficiency instead of feats like Spells Known or Evasion or Poison, etc. And in fact, I actually built a character that used such a cheat. I built a Psion with a level of Cleric which gave me the two armor feats and a bunch of other utility. I have also seen combat Clerics with Heavy Armor. \$\endgroup\$
    – Gates VP
    Commented Jun 10, 2014 at 21:41
  • 2
    \$\begingroup\$ @GatesVP That's... not a cheat by any stretch of the imagination; Cleric 1 is certainly a formidable level often worth considering, but for a psion that does put you considerably behind. And no, the classes aren't balanced, and the feats even less so. \$\endgroup\$
    – KRyan
    Commented Jun 11, 2014 at 1:24
  • \$\begingroup\$ @KRyan total aside, it was actually a useful trade-off, the Psion goes from "Wizard-speed" to "Sorcerer-speed" on spell progression, but it converted my character from "glass cannon" to "brass cannon". I made the dip after level 10 as we had hit the point where the pointy stick had AC about 17 greater than mine. Full plate closed a much of the AC gap, Cleric gave a +2 Fort boost and Vigor + Channel + CLW gave me the ability to live through a fight or two :) \$\endgroup\$
    – Gates VP
    Commented Jun 11, 2014 at 4:18

No, I don't think it seems flawed.

Mithral is an almost magical material, legendary for being lightweight without losing strength, and someone who is an expert at wearing armor should be able to wear a breastplate made out of it without penalty.

My first thought when I think about a mithral breastplate is the main character's armor from the movie A Knight's Tale (fun movie, you should see it if you haven't). In this case, it's a very well-made piece that allows him full motion and doesn't slow him down much at all... That's a masterwork breastplate, roughly. Mithral supercharges that.

Regarding the mechanical side... I honestly have no problem with that either. Using the Fighter as a balance point is a fairly bad way to go about things anyway, and Rogues are generally going to an AC close to the Fighter's past early levels (if only because they're boosting Dex anyway generally).

A rogue in +5 Leather armor with an 18 Dex and a +6 item boosting it is going to have an AC of 23, vs a Fighter in +5 Full Plate with 10 Dex having an AC of 24.

If the rogue gets, say, a Mithral Chain Shirt instead of Leather (which is a suitable Roguey item, I think), his AC is now 25. The fighter might have some Dex, I guess, especially with armor training, which could put him ahead, but that's gold spent on items (or points spent on abilities) that could be going towards his main trick (assuming he's not Dex-based)... And the rogue could get a Book of +Dex, or be a race that gets +Dex, or just be putting his ability score bonuses as he levels up into Dex as well, putting him ahead again.

In conclusion... I don't think that the Mithral Breastplate being good for rogues is a problem. Mithral Breastplate + Armor Expert is strong, but fine, balance-wise. The rogue can already keep up in AC anyway.


I think it's worth actually digging in to the details here as there are several trade-offs. Let's run the numerical comparisons, assuming a character at level 8+ so that the +6 Dex mod is realistic.

Mithril Chain Shirt with max dex (6)

  • 0 Feats
  • Cost: 1100gp
  • Armor Check Penalty: 0
  • Speed Penalty: 0
  • Max AC Bonus: 10 (4 armor + 6 max dex)
  • Touch AC Bonus: 6
  • Flat-footed AC Bonus: 4

Mithril Breast Plate with max dex (6)

  • 1 Feat + 1 Trait (light armor + armor expert)
  • Cost: 4100gp
  • Armor Check Penalty: 0
  • Speed Penalty: 0 (treated as light)
  • Max AC Bonus: 11 (6 armor + 5 max dex)
  • Touch AC Bonus: 5
  • Flat-footed AC Bonus: 6

Mithril Full Plate with max dex (6)

  • 3 Feats (light/medium/heavy armor)
  • Cost: 10500gp
  • Armor Check Penalty: -3 (on lots of skills)
  • Speed Penalty: -10 ft (treated as light)
  • Max AC Bonus: 12 (9 armor + 3 max dex)
  • Touch AC Bonus: 3
  • Flat-footed AC Bonus: 9

Note the key trade-offs here that we're balancing out several types of AC along with monetary cost and feat cost. And there's the cost of getting to +3 or more Dex mod. For some classes this is basically their mission for others it's not.

I personally think that Mithril Breast Plate + Armor expert is a nice hack for Dex-based characters, but not really "broken". Most Dex-based classes already get light armor feat, so you get a better Max AC and a better Flat-footed AC for the cost of one trait and 3000gp. However, it's clearly not free and that 3000gp can get you a +1 AC elsewhere via Ring of Protection or Amulet of Natural Armor.

The extra bonus from a high DEX is that you also get a good Reflex save.

Personally, the comparison highlights to me that Full Plate is pretty sub-par. You need 3 Feats to use it effectively and it's really expensive. And even if you do it correctly, you still suffer movement penalties and penalties on all kinds of useful combat skills like Acrobatics and Stealth.

The net result is that for about the same money and feat cost, Rogues and Fighters will be within a couple of points for Max AC.

  • \$\begingroup\$ Could you include a fourth entry for full plate with no feats in armor proficiency? \$\endgroup\$ Commented Dec 2, 2014 at 6:24
  • \$\begingroup\$ If you do fullplate without the feats your Armor Class Penalty is also applied to your attacks. That's a huge penalty that renders full plate nearly unusable without the proficiency. \$\endgroup\$
    – Gates VP
    Commented Dec 2, 2014 at 8:06

If this legal combination offends your GMing sensibilities, then perhaps you could house-rule that Armor Expert only applied to armor the character is profficient with. After all, it would be difficult to be an expert with something you aren't familiar with.


It is not flawed by any means. It is open to preference.

If you were a fighter your Armor Training would pay off at 15th level and you would have benefited more from another material like Adamantine for damage reduction. When we compare the fighter to the rogue we can assume that they are both capable of buying identical items. Thus they both have the same nat armor bonus, deflection bonus, armor bonus, etc. The only thing to take into consideration would be the bonus from Dexterity. A fighter in Breastplate (Non-Mithral) at level 15 will have 6 armor + 7 max dex = 13 total. A rogue with Mithral Breastplate will have 6 armor and 5 dex = 11 total.

Heck a fighter of 3rd level with Full plate will have 9 armor and 2 dex = 11 total. That is on par with the Rogue wearing Mithral only for 2700 gp less.

Cost for Mithral Breastplate:
Cost: 4200 gp
AC Bonus: +6
DEX Bonus: +5
Armor Check Penalty: -1
Spell Failure: 15%
Speed: 30 ft.
Weight: 15 lbs

You are paying 4,000 gold for +2 extra max dex bonus, +3 armor check penalty, -10% spell Failure chance, +15 ft speed, and -15lbs. That is not all, in order for the Max Dex bonus to be beneficial you would need to have 18-21 dex.

It is good yes, but it is not flawed. It simply favors some classes over others. Some may prefer to spend the gold or the trait in other places.

Side Note:
I was unaware at first about the armor check penalty being applied to non proficiency. But I found where you read that:

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. This decrease does not apply to proficiency in wearing the armor. A character wearing mithral full plate must be proficient in wearing heavy armor to avoid adding the armor’s check penalty to all his attack rolls and skill checks that involve moving.
CRB, pgs. 154-155

Just in case if anyone else was curious.


As it is legal in the Rules As Written, the only question remaining would be if this is sensible, meaning if you as a GM should allow that.

You could argue that having the Armor Expert trait and not having any Armor proficiency at the same time is questionable. How can someone be an Armor Expert and not be proficient with any armor at the same time? Where did he get that expertise?

So if you really wanted, you could house-rule that he still needs the appropriate Armor proficiency (or at least ANY armor proficiency) to get the armor check penalty benefit of Armor Expert.

  • 2
    \$\begingroup\$ I don't understand what you're saying here. How is he supposed to rule that the player needs armour proficiency? The point of the question is that the normal nonproficiency penalties for armour don't apply to armour with an ACP of 0. If you are suggesting a rule that changes that, could you explain what the rule change you're suggesting is? \$\endgroup\$
    – DuckTapeAl
    Commented Jun 3, 2014 at 17:02
  • \$\begingroup\$ @DuckTapeAl I did an edit to make explicit what they're implying. (That ACP won't get to 0 in the first place if they don't get the benefit of Armor Expert.) Better? \$\endgroup\$ Commented Jun 3, 2014 at 22:52
  • \$\begingroup\$ I'm not convinced that that was what he was implying. If he comes back and clarifies, then I'd reverse my -1, but I don't want to do that if I don't know what his intention was. \$\endgroup\$
    – DuckTapeAl
    Commented Jun 4, 2014 at 17:59
  • \$\begingroup\$ I edited for clarity that i mean a house-rule in the name of "making more sense". I have been playing some other systems side by side with Pathfinder for some time now and other systems are not half as thorough with the rules, so you have to make "sensible" decisions like "this can't go without that" all the time, because none of that is in the rules. \$\endgroup\$
    – Oliver
    Commented Apr 27, 2015 at 12:02
  • \$\begingroup\$ So you're saying you'd not give him the benefit of his trait and apply at least the -1 penalty to hit anyway? Would you at least refund the trait or what? \$\endgroup\$
    – Julix
    Commented Jan 23, 2016 at 9:56

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