It's not (as in, Raz is right). PDR1 would do nothing. PDR5 might require 8 hits on account of it being potent enough to count as an ADR1 weapon, and thus causing damage to something on the armor scale.
Regarding that example that is being bandied about... it means it has 8 SP and is Armor grade. Perhaps I should remind people I actually created DRv2? Don't rule-lawyer me on my own system. Even if I think hit points are kind of crap nowadays. >_>
So, regarding what I was asking Zack, I was saying "say we're being nice and actually assuming the pack is worth 5SP and its resilience is on the armor scale (meaning PDR5 weapons or better hurt it), I was asking Zack "hey, is it made of durandium? If so, please apply the modifier to the SP". Because with 5 SP on the armor grade, you're litterally equivalent to where an Harpy could be. I'm pretty sure it takes an Harpy - as brittle as it is - more killing than a pack like this would.
Also, Zack, choose Bubble, or Conformal, but you don't get to have 2-facings on something that's barely a power armor and much less a tank/shuttle. That's the last time I'll ask.