Thomas Prufer wrote:
http://www.ikea.com/gb/en/catalog/products/50153123/

2mm x 37 cm x 29 cm, 2 quid pack of two, polyethylene.

The nice thing about Ikea is they tell you what everything's made of, and
decent dimensions. Those look interesting, though I'm curious what
'bendable' means. Hopefully they're not floppy...

I've seen temporary signs made of plastic shaped like cardboard: two flat
surfaces and a wavy bit in between. Usually cable-tied to things, easy to
remove the eyesores...

You mean estate agents' boards and the like... interesting thought. We have
some foamboard (expanded polystyrene sandwiched between two flat surfaces)
that's intended for artwork mounting etc... works quite nicely but the foam
retreats back into the core around cut surfaces, so cuts aren't very rigid.

Theo