This question is mainly for me looking at the different feats and class powers I have with a Solarian build I'm going for. Without going into too much detail, I have a Soldier 1/Solarian 4 with Blitz (because, of course I do) and I've been looking at my level 5 feat, figuring out what I want. Since I am getting my second revelation at the same time, I saw Dark Matter being there and thought…DR is nice. But then I see the feat Improved Resistance, which also gives me DR…without being attuned…and at my full level rather than half Solarian level.
I'm not looking for advice here. More to the fact, I'm wondering if taking Improved Resistance for Kinetic would stack with my Dark Matter. Chances are, it won't, but I'd like to know fully, and if there's a rule in the book somewhere that describes this, please list this too.
Best Answer
No, it doesn't stack.
As per the SRD or on page 263 of the core rulebook:
Basically, unless your source of damage reduction explicitly clarifies that it stacks with or improves existing damage reduction, they don't stack; you just get the benefit of whichever one is most useful against a given attack.
Both the Enhanced Resistance feat (at least when choosing kinetic damage) and the Solarian Dark Matter ability offer DR/-, meaning it's not negated by anything and applies to all kinetic damage. The bonus offered by Enhanced Resistance will always be better than the one offered by Dark Matter, so the latter becomes redundant if you have DR from the former.
It is important to note that though the feat offers better DR, it can only be taken once - the feat does not specify that you can take it multiple times and choose a different option, so the powerful resistance it offers can only apply to one kind of damage. Since the Solarian offers you a different, albeit weaker, source of DR, accepting somewhat worse kinetic damage resistance in exchange for pretty good energy resistance could be well worth it.