I've heard comments that energy damage, or particularly acid damage, somehow bypasses object hardness - either fully, or in half. However, I haven't found a consistent citation or interpretation for this.
Does it really?
Role-playing Games Stack Exchange is a question and answer site for gamemasters and players of tabletop, paper-and-pencil role-playing games. It only takes a minute to sign up.Sign up to join this community
No, it doesn't bypass hardness at all.
(This may have been different in D&D 3.x, but it isn't the case now.)
The acid descriptor rules don't suggest acid damage gets any special handling, nor do the rules on hardness. There's rules on what energy damage does to objects, though - and from the notes on damage in d20pfsrd, acid damage is considered energy damage - but these rules don't add anything about bypassing hardness:
Energy attacks: Energy attacks deal half damage to most objects. Divide the damage by 2 before applying the object's hardness. Some energy types might be particularly effective against certain objects, subject to GM discretion. For example, fire might do full damage against parchment, cloth, and other objects that burn easily. Sonic might do full damage against glass and crystal objects.
In fact, this suggests energy (including acid) damage deals less damage to objects usually: you halve the damage before doing anything, and half damage is the most it can deal, and then you apply hardness, so it might deal even less than that.
At GM discretion, energy damage can still retain its full damage amount depending on the situation, such as if you're using fire on wood. It's ambiguous whether they mean "deal full automatic damage, ignore hardness" or "just don't halve the damage before applying hardness", but since this is an explicit written author's suggestion to ignore the rules, trying to figure out to what extent the rules are advising us to ignore them is probably not worthwhile. Just use your discretion and break them whichever way you prefer given the situation.
Other than GM discretion, there's no damage bypass, nor half-damage bypass, etc.
In Pathfinder, energy damage specifically deals half damage to objects and does not bypass hardness. But there are some exceptions here.
Take a look at the 2nd-level spell Shatter.
...you can target shatter against a single solid non-magical object, regardless of composition, weighing up to 10 pounds per caster level.
However, if you are using the excellent Psionics module from Dreamscarred Press, they do have a [sonic] damage type that bypasses hardness. Here's an Energy Ball for example:
Sonic: A ball of this energy type deals –1 point of damage per die and ignores an object’s hardness.
Most of the "powers" that deal energy damage allow you pick the type (with some restrictions) so this is a ready option for most Psionic characters.
Clearly, you're doing less damage here, but 8d6-8 is still around 20 pts of damage. That's 10 damage after "half energy", but with the hardness bypass, it's enough to take out 1 inch off all of the wood in the blast radius.
According to this, sonic damage bypasses hardness.