(FORTUNE Magazine) – The ugly poly-blend curtain separating coach and first class is a fixture on airplanes. But ever wondered what purpose it really serves?

Airline reps' lips are tighter than an economy-class seat. Virgin Atlantic had no comment, Delta didn't return numerous phone calls, and US Airways and American would say little more than that it's for "privacy." So much for the friendly skies.

Finally, someone spilled. "It remains one of the last bastions of true class separation," says Kiki Ward, a former American Airlines flight attendant. First-class passengers get freebies like vodka tonics, DVD players, and manicures--perks that, if seen, might enrage coach passengers who are choking down a little bag of stale peanuts. Acknowledges Nalini Fernandes, a Cathay Pacific flight attendant: "It's mainly there to prevent riots and stampedes." Who knew polyester was so powerful?

--Reed Tucker