Danno- Use sections of (used) overhead or Xerox clear sheets. It MUST be the kind that survives heating in the xerox machine- then will not melt in epoxy or polystyrene resin OR stick to it. The trick is to get the right amount underneath as you are rolling on your piece of film- and taping down the edges. Not too little = air bubbles-- not too much = bumps. But it will be glass smooth in the morning!