Traveling transatlantic both ways recently, both times upgraded to Premium Plus with Plus Points (and yes, both times they took 40PP instead of 20, so I shall have to get them back — why does this always happen?!).

One way was on a 787. I was quite cold and used the blanket a lot.

The other way was on a 777 type 77E. I was reasonably warm (but still used the blanket) and was struck how, every time I went back to the lavatories, stepping into Economy was like an expedition to the Antarctic — a large drop in temperature between row 22 (back row of PP) and 31 (front row of Economy Plus). It made me shiver. I had never been previously aware that it was even possible to have such massively different temperatures in different but adjacent parts of the plane. I found myself wondering whether those in the back were in a colder zone in order to save the airline money, but surely it can't make that much of a difference?

Some widebodies are divided into zones, each with its own thermostat. So the temps can vary significantly within the plane depending on who controls it (sometimes pilots and FAs AFAIK).

I�d be very surprised if they dictated the temperature within the zones though and even more surprised if it were to actually save money.