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Originally Posted by
Shishizaru
Sort of. As mentioned before, passive DR overlaps, but does not stack.
For example, say you have Stoneskin (DR 10/Adamantine) and Ironskin Chant (DR 5/-) active. If something hits you with a non-adamantine weapon, you do NOT have 15 total DR. You get 10 from Stoneskin, since it is a higher value that Ironskin Chant. If, however, something with hits you with an adamantine weapon, it will bypass your Stoneskin. It will NOT bypass Ironskin Chant (as nothing does), so you still have 5 DR. Ironskin Chant effectively shores up Stoneskin's "weakness," but will not help against things Stoneskin already protects against.
As far as Epic Ring of the Mire is concerned, it only protects against pierce damage. It might be nice to swap in if there's hordes of archers about, but it does nothing to stop slash/bludgeon damage, so I would not recommend it as your general purpose DR item.
Note that blocking DR (from the shields you mentioned earlier) WILL stack with passive DR if you are blocking.