This variation on the many demos of Boyle's Law always gets a good reaction from my students.
It was devised by a particularly physics-fun-loving group of 6th years a few years ago. When I was running the standard partly-inflated-balloon version, they wanted to know if the same thing would work with a plastic bottle. I said it probably wouldn't, because I assumed the plastic would crack in a few places when it was crushed - but they persuaded me to try anyway and I'm glad they did.
Its actually astonishing how strong these bottles are. I've been able to re-inflate and re-crush the same bottle over and over again without any crack appearing. And the bottles have the advantage over balloons that they're everywhere! (I know that's not really a good thing - but they can be easier to put your hands on than a balloon, so its good educationally even if it is a environmental disaster...)
In retrospect, it seems like an obvious idea - and maybe everybody else has been doing this for years?
Either way, I had fun playing around with the viedo-editing software!