Who says insulating paper is resistant to pressure?
The insulating paper that permeates the electrolyte is only the negative plate, and the insulating layer is the oxide layer of the outer layer of the positive plate.
As for the shiny aluminum foil is the negative lead.
When the electrolytic capacitor plus reverse voltage, it will layer that layer of decomposition, so the leakage,
If the long-term increase in a small amount of reverse (to ensure that the capacitor will not explode), even in the negative aluminum foil on the establishment of oxide,
So that the polarity of the electrolytic capacitor is reversed.