Damage reduction of the same type stack.

[Jeff Clem]

Does damage reduction of the same type stack? ex. magic/5 from to different sources.

[Cuuniyevo]

No. CRB page 562 says, "If a creature has damage reduction from more than one source, the two forms of damage reduction do not stack. Instead, the creature gets the benefit of the best damage reduction in a given situation."

[Bob Bob Bob]

They don't stack unless they say they stack, Cuuniyevo quoted why not, here's one that does.

Armor Master Fighter wrote:

At 5th level, an armor master gains DR 1/— when wearing light armor, DR 2/— when wearing medium armor, and DR 3/— when wearing heavy armor. At 19th level, this damage reduction increases to DR 4/— when wearing light armor, DR 8/— when wearing medium armor, and DR 12/— when wearing heavy armor. This damage reduction stacks with that provided by adamantine armor, but not with other forms of damage reduction. This damage reduction does not apply if the armor master is stunned, unconscious, or helpless.