Warforged/Bladeforged get screwed with this cap.
MRR Cap- Different armor types can apply a cap for Magical Resistance Rating (U23):
Robes, Outfit, or empty armor slot: 50
Light Armor: 100
Medium Armor: No cap
Heavy Armor: No cap
WF/BF have to use a feat to take a body type beyond Composite (composite should be treated as light armor for PRR/MRR )
Mithral is treated as light armor even though it should be recognized as Mithral Medium Armor.
1. Composite Body should be giving the armor cap equivalent of light armor, it is base plating that has the properties of padded armor and treated in a similar way to how mithral moves the armor from medium to light, Composite plating moves the armor from light to none(effectively heavy robes).
Composite Body:
This plating is not natural armor and does not stack with other effects that give an armor bonus (other than natural armor).
This composite plating occupies the same space on the body as a suit of armor or a robe, and thus a warforged cannot wear armor or magic robes.
Composite plating also provides a warforged with a 5% arcane spell failure chance, similar to the penalty for wearing light armor.
2. WF/BF Mithral body is medium body plating made of MIthral wich moves it into the light category. This is why there is no actual selectable medium body armor option.
Mithral Body:
Docents you equip provide armor equivalent to Chainmail. This is treated as metallic light armor
(because it is Mithral, otherwise it would be medium armor, which is why WF/BF don't have a Medium Armor choice)
3. Adamantine Body:
Docents you equip provide armor equivalent to Full Plate.
This is treated as metallic heavy armor. You have damage reduction 2/adamantine, a 35% arcane spell failure chance, -5 armor check penalty to certain skills, and a +1 maximum dexterity bonus.
Note: Evasion doesn't work for Warforged with Adamantine Body since it is considered a heavy armor.
.. but of course the whole Mithral issue has been left unresolved for a while...
Cordovan posted earlier this year
No matter which way the WF/BF goes they are getting a disproportionate PRR/MRR recognition for the Composite/Mithral Body types.
I would like to see Docents/Composite Body removed from the game and have WF/BF just wear armor like everyone else.
They did it in the 4e rules for DnD..