Hi GannetI believe the type of plastic in question is polystyrene which is type No.6. But Tag is quite right it is very useful for scratch builds and dio's, you can also make your own sheet plastic, just follow Tags' recipe (I use Nitromors instead of liquid cement) and then when you have a squishy mess pour it all on to a clean piece of glass sheet,which has been wiped with a tissue dipped in Kleer or vaseline or some other release agent, then spread out and leave for a couple of days till dry. Hey presto Sheet Plastic, great for repairs, scratch builds, panels, modifications etc.
Enjoy
Regards
Bazza