Avid cardboards

The magician shows to the audience a coloured thin cardboard that, inside, contains another cardboard of different colour. In all there are four cardboards held one inside the other. In the last cardboard the magician inserts a white sheet of paper and closes all the cardboards again as to create a single package. To finish, after a magic gesture, he reopens all the cardboards and shows that on the last cardboard there is a real banknote in place of the white sheet.
Other ideas: you can change a blank playing card into the card chosen by the spectator. A sheet of paper will change into a business card. A 2 Euro coin will become a 20 Euro note.