Put the empty bottle and balloon in your refrigerator. Leave them there for at least one hour. They both must be cold.

     Before removing the bottle and balloon from the refriger- ator, prepare the buckets of hot and cold water. Add a handful of ice cubes to the cold water to make it colder.

     Taking the balloon in your hand, squeeze it to drive out any air it may contain. Then quickly slip the neck of the balloon over the mouth of the cold bottle.

     Immerse the bottle in the hot water (it’s okay if the balloon is in the water too). In a few minutes, you’ll see the limp balloon begin to inflate.

     When the inflation stops, immerse the bottle in the cold water. The balloon will slowly shrink and become limp again. Repeat the hot and cold immersion steps.