Is it impossible to fold a piece of letter-sized paper more than 7x?

  I was fascinated to see a program on MythBusters about paper folding. The theory proposed to the guys who run the show, Adam Savage and Jaime Hyneman, was that it is impossible to fold a piece of letter-sized (8.5″ × 11″, 216 mm × 279 mm) 20 lb (75 g/m²)copy paper with perpendicular folds [...]