Balloon hovercrafts are a fun thing to make. All you need is an old CD that you do not need anymore, a balloon of course, glue, and an old pop-up bottle top from a bottle. First, glue the bottle top to the CD on the hole in the CD. Make sure that the bottle top is closed! Then, blow up the balloon and without letting the balloon deflate, put it on the bottle top. Then open the bottle top and watch it hover!