The sins ref sheet talks about "armor classes" ranging between "v light" and "v heavy" and affects specific ship types (not specific weapon types). It is also not necessarily always good to have more armor - when facing bombers for example it seems you will take less damage if you don't have "v heavy" armor. The tech trees on the other hand give armor numbers. So if you tech up your fighters with +5 armor do they get "v heavy" armor and become vulnerable to bombers?! Does the armor number represent a simple subtraction from the damage of any weapon that gets through shields? (which would be the most intuitive)
Is there an armor FAQ?