Stalker0 said:
Swarms are supposed to be 1000's of tiny little creatures all biting you at once. Does that mean evne though they do 4d6 or whatever...that any amount of DR would render them useless?
It would depend on how you saw the DR working. Most adult humans probably have damage reduction to ignore the effects of a bee. Sure it stings, but it won't hamper you in any way. Now send 60 bees after someone and they can easily die.
Maybe you can describe DR as the ability to quickly heal your outer skin so anything that gets through your skin, does permanent damage (if that could be healed, you'd have fast healing). Anyway, if you have a hundred creatures attacking you, your DR ability would help, but probably wouldn't be able to recover from that many attacks or bites in a round. Therefore I wouldn't negate the damage.
Maybe your DR is caused by your armor. Well it that case, it makes sense to ignore the damage completely... unless there are any cracks, seams, or crevices in the armor. If they can get at your neck, under face mask, under your arms, behind your knees, etc. then it would make sense for the DR not to negate every swarm. So a warforged that took the adamantine feat would ignore it all. A fighter with adamantine breastplate wouldn't. A barbarian... well I don't know.
According to the rules, the swarm does damage as a whole so DR applies normally, but doesn't negate the damage completely. I'd just stick to that and try to explain it with the possible scenarios above.