How do Armors and Shields with special abilities with no bonus stack?

Question

I am not sure how some of the magic special abilities of armors and shields work.

Is an element resistance on an armor or a shield (e.g. acid /10) a bonus or is it not considered a bonus? (there is a cost but no specification of bonus)

Reading the DM manual I have the impression that I could create this item:

Armor/shield +1 (2k) with greater resistance to every element (66k x 5). The armor would be considered as a +1 bonus armor. Is this possible?

Answer 1

You definitely can create a +1 armor of greater acid/cold/electricity/fire/sonic resistance or a +1 shield of greater acid/cold/electricity/fire/sonic resistance. This would cost approximately 2,000 gp for the armor or shield,¹ plus 5×66,000 gp. That’s 332,000 gp total.¹ Either item would absorb 30 points of damage of each energy type per attack, potentially reducing an attack by up to 150 damage (if you somehow manage to get hit by an attack that deals 30+ damage of each energy type).

Both items would still be considered +1-equivalents, which means that adding another +1-equivalent property would cost 3,000 gp (2²×1,000 gp − 1²×1,000 gp = 4,000 gp − 1,000 gp = 3,000 gp). The flat-cost resistance properties do not cause any of the quadratic growth in cost that you see from +X-equivalents.

First problem: items with a value above 200,000 gp are considered epic. That means whoever makes it (or adds properties that bring its value above 200,000 gp) need to have Craft Epic Magic Arms & Armor, which requires 25th level. That can be hard to find. Not an issue in a theoretical sense, but worth mentioning.

Second problem: Getting both the armor and the shield is pointless:

Multiple sources of resistance to a certain energy type don’t stack with each other. Only the highest value applies to any given attack.

^{(Rules Compendium pg. 48. Note: Core is ambiguous and Rules Compendium vs. Core can be contentious)}

1. _{Plus whatever the base cost of the mundane armor or shield itself is, plus 150 gp for being masterwork.}

Answer 2

Resistance is a special ability, not an enhancement bonus

Here is what the rules say (emphasis mine):

In addition to an enhancement bonus, armor may have special abilities. Special abilities usually count as additional bonuses for determining the market value of an item, but do not improve AC. A suit of armor cannot have an effective bonus (enhancement plus special ability bonus equivalents) higher than +10. A suit of armor with a special ability must have at least a +1 enhancement bonus.

The special abilities do not always add an enhancement equivalent bonus, only usually.

If you then look at the table for armor special abilities, you can see that for some of them in the column "base price modifier" an enhancement bonus equivalent is given, for example spell resistance comes with a +2 bonus and a little footnote marker ¹. That footnote informs you that

¹ Add to enhancement bonus on Table: Armor and Shields to determine total market price

Others do not have an enhancement bonus and footnote, they instead have a fixed gp value cited. This is the case for acid resistance, at a price of "+18,000 gp". So in those cases, you do not add an enhancement equivalent bonus to increase the effective bonus that the weapon has for determining the price, you use whatever normal enhancement bonus (or bonus from other abilities) it has, and then add a lump sum. These enhancments have no "special ability bonus equivalent" to add. Your item needs to have at least a +1 bonus to start with, as per the rule given above.

This means for your example, you could create a +1 armor that would cost the armor's base price plus 1,000 gp for a +1 enchancemnt bonus, and then for each +66,000 gp, could add one of the greater resistances. The total price would be 332,000 gp plus the base price of the masterwork armor.

There is no stacking involved in this case. If you also had a +1 shield (costing another 1,000 gp plus masterwork base price), the shield's enhancement bonus would stack with the armors enhancemnt bonus of +1 for at total of +2 enhancement bonus to AC, because the rules inform you that:

Shield enhancement bonuses stack with armor enhancement bonuses.