Hot Air Balloon

Roll a paper napkin into a tube and twist up the top. Stand it upright and light the tip. While the lower part is still burning, the ash formed rises into the air. 

Take care! The air enclosed by the paper is heated by the flame and expands. The light balloon-like ash residue experiences surprising buoyancy because the hot air can escape, and the air remaining in the balloon becomes correspondingly lighter.

Veryfinenapkinsarenotsuitablefortheexperiment because the ash formed is not firm enough.