I've managed to salvage quite a few sheets of 25-30mm thick polystyrene packing material. It is easily cut to TBH follower board size and will act as excellent insulation in the empty ends of a hive. I have some already cut, and by taping together the cut-off bits it is possible to get two out of most sheets - or maybe three if you are using the Weston mini TBH design! It can also be laid on top of the bars as insulation under the roof. If you are interested I will ferry some of it home and we can discuss how/when to get it to you. The nights are getting ever colder so I suspect it will be needed sooner rather than later.