DR Stacks with itself but the greatest piece should be noted in Parenthesis. Yes this means Barbarians at DR1, about to gain DR2 will gain a total of 3 DR. No it doesn't make them into tanks.
DR is ALL DR/-. No much hunting for odd DR types, having to lug around golf bags of different weapon types, or just bypassing it all with great magic weapon. DR/magic critters rejoice!
