What effect does combining Mithril and an Armored Kilt have on armor category?

Question

I have a few questions regarding the interaction between Mithril and Armored Kilts in Pathfinder. I would like either official sources, or the words of pathfinder creators/developers if possible. I'm hoping to find good rules basis to convince my GM that a mithral chain shirt with a kilt will wind up still being light, but I'll accept if the rules or developer commentary states otherwise.

My thoughts below come from the fact that if medium and heavy armor is made with Mithril (e.g. a Mithril Breastplate), it is considered 1 armor category less than what they usually are. This affects properties such as movement speed.

Adding an Armored Kilt to armor, on the other hand, raises the armor category by 1.

So let's say you have a simple chain shirt. If you put a kilt on it, it counts as medium armor.

• Now if that is a mithril kilt, would it still make the chain shirt count as medium armor in terms of movement speed reduction? And if yes why?

• Alternatively if you put a normal kilt on a mithril chain shirt, would it still become medium armor in terms of movement speed reduction?

• And lastly if you put mithril kilt on a mithril chain shirt would you still get medium armor's movement speed reduction?

I would like to add that the armored kilt table itself does not mention or specify any movement reduction. So for me there is the chance that the armored kilt might not even make the armor slower even if it increases it's category by 1.

---

Please do not answer simply with the train of thought that it goes:
Chain Shirt (light) -> Mythril Chain Shirt (Still light) -> Kilt makes light into medium.

I am looking for an answer with quotes from rules and developers.

Answer 1

Mithral Chain shirt would be Medium (treated as light for all but proficiency)

The relevant parts of Mithral are:

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.

The relevant part of Kilt are:

When you add an armored kilt to a suit of light armor, the set counts as medium armor. Likewise, a kilt and medium armor counts as heavy armor. Adding an armored kilt to heavy armor has no effect.

Firstly lets address: "I would like to add that the armored kilt table itself does not mention or specify any movement reduction." Once you stop using a kilt as a piece standalone armor the rules stop caring about what category of armor used to be. (making Mithral kilts irrelevant) It is now part of the new armor (Sean K Reynolds says that you cannot stack enchantments with a +X on a kilt. He is the best authority we have for now, and it supports common sense)

A kilt adds one to the armors category for all purposes when you attach it (including movement). If you somehow managed to make a kilt that was medium and it had the above rules text it would still only add one to your armors category. Noticeably, this means you require proficiency in the new category of armor. (Medium for the Chain shirt)

Mithral does not actually modify the armor category. It allows you to treat it as lighter for purposes of movement and other limitations. Mithral and Kilt have no actual interaction.

In summary:

• Kilt: Add one to armor category for all purposes
• Mithral: Pretend its one lower for all restrictions (except proficiency)

Thus the following combinations are possible:

Gear: Treated as for restrictions(Proficiency required)

• Light Armor w/ Kilt: Medium(Medium)
• Light Mithral Armor: Light(Light)

• Light Mithral Armor w/ Kilt: Light(Medium)

• Medium Armor w/ Kilt: Heavy(Heavy)

• Medium Mithral Armor: Light(Medium)

• Medium Mithral Armor w/ Kilt: Medium(Heavy)

• Heavy Armor w/ Kilt: Not possible

• Heavy Mithral Armor: Medium(Heavy)
• Heavy Mithral Armor w/ Kilt: Not possible

To throw in a little common sense
The kilt should probably be made from Mithral if the armor is made from Mithral to allow Mithral to apply. This is in no way RAW however.

Additional Source

Answer 2

Rules as written

There are three parts of the rules to consider:

• The Armor Table tells us that the armored kilt and the chain shirt are light armors.

• Making a suit of light armor out of mithral explicitly does not change the armor category (emphasis mine):

  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.

  So even if there was a "lighter than light" category, it wouldn't apply for mithral light armors. So both the mithral chain shirt and the mithral armored kilt are still light armors.

• Armored kilt itself states

  When you add an armored kilt to a suit of light armor, the set counts as medium armor. Likewise, a kilt and medium armor counts as heavy armor. Adding an armored kilt to heavy armor has no effect.

  There is no special rule for mithral armored kilts, nor for adding an armored kilt onto mithral light armor.

This means that any combination of light armor (including mithral light and medium armors) and armored kilts (both regular and mithral) counts as medium armor, with no room for discussion.

Developer statements

James Jacobs, the creative director has multiple things to say about armored kilts in his AMA thread on the paizo boards

Mithral does not have any effect on the "lightness" of an armored kilt

James Jacobs, Creative Director

harmor wrote:

Therefore the Mithrilness of an Armor Kilt does nothing when increasing the armor's effective type? [...]

Mithralness doesn't really do much at all for armored kilts, honestly. Because armored kilts are weird and don't work the same as armor, so mithral doesn't work the same on it. [...]

Armored kilt + mithral medium armor = effective medium armor with need for heavy armor proficiency

James Jacobs, Creative Director

harmor wrote:

Do you need Heavy Armor Profiency to wear a Mithril Breastplate + Mithril Armored Kilt? Are you lightly or mediumly encumbered as a result?

[...] making an armored kilt mithral doesn't affect the fact that you're still wearing more armor than you normally would. A mithral breastplate is light encumbrance, but that plus a mithral armored kilt is medium encumbrance.

harmor wrote:

Thanks. What about the required armored proficiency?

[...] If an armored kilt increases the armor's effective type from light to medium or from medium to heavy, you need proficiency in the final result in order to effectively use the armor.

Note: Omitted from the snippets were mostly statements showing that James Jacobs absolutely despises the armored kilt and suggests removing it from the game entirely. This is also the reason why it wasn't reproduced in the ISWG (directly stated by him) or (presumably) Ultimate Equipment.