making armor one category lighter

[_RAGNAR_]

Besides mithral are there any enhancements that do this?

[Quentinas]

There is halfweight from Underdark that reduce the category to light so it depends on the starting armor if is only one step or two

[Troacctid]

Blue ice (http://archive.wizards.com/default.asp?x=dnd/ex/20040911a&page=5) does it cheaper than mithral.

[Ramza00]

Arms and Equipment Guide has Tessellated Armor. It is a full plate that is in a "magic" box and when you say the password it assembles onto you Iron Man 3 Style.

11,560 gp cost (half that plus xp to craft)

+8 AC*
-4 Armor Check Penalty
+1 Max Dex
25% Arcane Spell Failure
Counts as Medium Armor not Heavy.
Once a day do Hypnotic Pattern

Now the Armor has some changes which I underlined, reducing the ACP, ASF, and counting the armor as medium.

*Lastly it is a +2 Armor which means per the MIC you can reallocate that +2 to armor enhancements or you can improve your +8 AC even further. In effect the armor is 7560 gp in cost and the +2 makes it 11560.

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Surely we can also stack Mithril on the Tessellated Armor getting these extra benefits for +4000 gp.
-1 Armor Check Penalty after change
+3 Max Dex after change
15% Arcane Spell Failure after change.

[Jopustopin]

Someone with the dragoncrafter feat can make dragoncraft armor it reduce the category of armor down one category.

[Dimers]

Glassteel in CoV is functionally equivalent to mithral, including the category change. Shadow silk in ToM and darkleaf in AEG both do the job too.

[rrwoods]

It's pretty likely that the calculator at http://www.wdtaylor.net/calculator.html covers whatever it is you're looking for!