Mechanics Question:Damage Immunity

[Twelve]

If this is in the wrong spot, I apologize, please feel free to move it accordingly, send me a link to the right forum post or send me a PM about what a horrible, rotten, low-life, good-for-nothing piece of.... you get the idea... anyhow; my question is this:
 
Damage Immunity - does it stack?  Please explain.
 
Example:  A generic (non-perk) barbarian has 10% damage immunity at level 5.
 
A set of chainmail gives "slashing 5% immunity".
 
When worn, how does this play out mechanically?  Is it over-ruled by the 10% or does it become 15% for slashing, and 10% for everything else>  Or something else I am not considering in my current twelve pack-beer-consumed-state?  (pun intended)
 
Thanks
 
~12~

[VanillaPudding]

Yes. Damage resistance does not, however.

[Canzah]

To clarify VP's wisdom, in your example it does become 15% slashing resist whilst remaining at 10% for other physical damage.