In an attempt to expand a Coke bottle, I did the opposite - twice.
Firstly I put a Coke bottle in the oven to melt the plastic which I then took out and pumped with high pressure air blower. Due to the lower room temperature, the bottle quickly hardened and I didn’t achieve the desired effect.
So then I put a second Coke bottle in the oven which I was hoping to pump whilst inside via a mechanism that I made, but again failed because the pressure was not sufficient.
It’s interesting to see that even though the bottle was deformed in both cases, you can still distinctively tell that they were once Coke bottles.