When I was in college, my Stage Craft teacher showed us this. Basically the machine heats up a sheet of plastic, and once it’s malleable enough it’ll be blown up to make room for whatever you want to imprint in the plastic. Once it’s in place, the air reverses and the plastic vacuum-sucks all around the object.
He demonstrated it on a baby doll and it was like a baby had been frozen in carbonite. I got to take it home and I still have frozen-carbonite-baby to this day (his name is Franklin XD)