Years ago if you looked at the back of a fridge you'd see the
condenser coils. When I was looking for a new fridge recently I
noticed that most models have the back covered with a sheet of what
looks like corrugated plastic. I assumed that this was for protection
and would be removed on installation.

Not so - my new replacement does not mention removing the back and
wouldn't be straightforward. I thought that condensers should be in
open air for efficiency. What's going on?

NB the entire back is covered apart from a 20 cm gap at the bottom
where one can see the compressor etc.

GrahamC