If you choose to use the paper napkin, I would recommend leaving it folded. Something like a cocktail napkin might work best since they are a bit stronger. A napkin that is very thin might not be a very good idea, especially if you perform the version where the spectator does the work. For a completely impromptu version, the shirt version shown in the trailer is really about the best. It's not taught on the DVD, but the effect is performed exactly the same way.