.... and speaking as a hobby Moviemaker, polyester needs a tape or Ultrasonic $plicer, while acetate can be spliced with good old Film cement. The Poly movie print stock often has an almost iridescent look on the roll due to the antistatic coating on the back.

A film jam on Poly is also likly to damage the equipment as Poly will not tear easily.

I have heard that some folks find that slides on Poly stock will not work in some mounting machines as the film needs a very sharp blade to cut cleanly.