Fustian was originally a coarse cloth, later a higher-grade twill. The word comes into English from the French fustaigne. The etymology is conjectural, but one explanation is that it derives from the medieval Latin fustaneum, from pannus fustaneus, "cloth from Fostat," a suburb of Cairo where the stuff was manufactured.
A further conjecture is that the sense progressed from mere cloth to bombast because fustian was used to cover pillows and cushions, and thus took on a sense of padding.
Whatever the origin of the word, we recognize the verbal kind when we see the turgidity.
Example: From Georgette Heyer's The Grand Sophy: "Pooh!" said Sophy. "Mind your horses, Charles, and don't talk fustian to me."