I too believe modern electrolytic caps no longer use paper, but we must remember some of these units we're talking about are approximately sixty years old!
Circa 1975, a tech where I worked managed to wire a high current, low voltage power supply with a bunch of 2000 uF filter caps installed with their polarity reversed. When he threw the switch, there was a loud ka-PLOW! Amidst the smoke, bits of aluminum foil were fluttering around the lab almost up to the ceiling -- sort of like the chaff to fool radar in WWII. Wish I had a photo of the look on his face; no doubt one of his more memorable learning experiences.