Several of the new ship modules in Disharmony give "Hull Weakness X%".
What is Hull Weakness? Should I be worried?
Defence Type & Hulls
Since the release of Disharmony, the different hulls have a new property called Hull Weakness, which modulate the received damage: the lowest hull weakness is, the more resistant the hull. A large ship has 100 Hull Weakness, a medium 200 and a small 300. The damage modulation is directly related to the value of the defence: the higher the defence value, the more efficient is a low hull weakness. With this new patch, Deflector has the highest defence value, then shield and finally flak. So that means that a large ship receives a better protection from deflector than flak because of the final impact of hull weakness will be lower in the first case.