Gansk said:
OK, substitute "-" with "adamantine". Same mechanic?
I am not sure I understand your question. Let's try this basic primer on the difference between DR and Hardness.
Basically hardness and DR sometimes have similar end outcomes but they aren't the same thing.
Usually Objects have Hardness.
Usually Creatures have DR.
Hardness reduces almost every sort of numerical hit point damage that an object can take, but a few things (notably adamantine) can bypass hardness to a certain extent.
DR behaves similar to hardness in that it reduces numerical damage from certain forms of attack, primarily:
1. physical blows (swords, clubs, claws etc.)
2. spells and magical effects that are similar to physical blows (spiritual weapons, conjured stones etc.)
DR does not reduce the damage from most spells and supernatural effects that grant saving throws and are basically energy based, such as fireballs or breath weapons for example.
DR comes in two basic flavors: breakable and unbreakable. Breakable DR is further subdivided by what breaks the DR (magic weapons, alignment, weapon type or weapon material).
Unbreakable DR (i.e a DR of X/- where x is a whole number greater than 0) is actually a misnomer. It is not really unbreakable, it is only unbreakable by weapon types. Energy attacks (see above) still ignore it the same way they ignore all other DR, so it is still well short of the impressive protection that is hardness.
Note however, that in one specific instance, DR x/- is better than Hardness X and that is against an adamantine weapon. An adamantine weapon ignores hardness up to a certain level (19 I think) , it does NOT ignore DR of any type other than DR x/adamantine. So while hardness 15 would not stop a 10 point hit with an adamantine hammer, a DR of 15/- WOULD stop that blow (so would DR 15/magic, alignment, cold iron, silver, piercing or slashing).
Tzarevitch