Why does a plastic bottle that is sealed at a high altitude change its shape when it is taken to a low altitude?

A plastic bottle changes its shape when taken to high altitudes or low altitudes because of the difference in pressure. High altitudes have low atmospheric pressure which by mechanical equilibrium expands the bottle. The pressure outside is less than the pressure inside which means to equilibriate the system, pressure has to move outward which makes the bottle expand.

Iwould you figure it out but you don't have a picture or in your question as to what the physical property you're looking for is

Aconductor easily transfer heat