I'm in the process of re-decorating. Wife wants polystyrene lining paper stuck on the walls before the new paper (who am I to argue!). It's an exterior wall, '70s build, and always feels cold to the touch. The lining paper is the type that B&Q sell and has polystyrene one side with a paper backing on the other. Okay, I'm going along with it but the question is once this stuff is up do I need to cross line it with normal lining paper before putting up the final wallpaper or do I paper direct onto it?