Leak Busters


    Kids, today we'll prove that helium leaks out from regular balloons and what can be done to stop it. Did you ever buy a balloon bouquet for someone? You probably know that you can't just make one yourself, because balloons filled with normal air don't float like the ones with helium do. And you may have already learned that this works because helium gas is lighter, or less dense, than the gases in regular air (nitrogen and oxygen). So you have to buy balloons filled with helium. But the gift shops now know certain tricks. Leaking helium molecules were a real problem for people who deliver balloon bouquets to parties. Their customers used to often complain that the helium balloons drooped within a day, or even overnight.

    Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

    You can prove that this droopiness is due to a gas leak by doing the following test. Get a regular balloon, a bottle of vanilla extract (or almond or orange), and a glass of water. Pour two capfuls of the vanilla into the balloon and then blow it up with air and tie it. Set the balloon on the glass so that the knot is under water. Leave this set-up overnight in a confined space, such as a closed bathroom or closet. Your nose should then help you solve the mystery. A balloon's surface has lots of tiny holes that can be seen only with powerful magnifiers, and vanilla molecules are small enough to eventually leak through this surface. Helium molecules are much smaller than air or vanilla molecules, and so they leak out even faster.

    What can be done to slow this leakage and make the balloons last longer? A chemist (a "leak buster") invented a chemical called Hi-Float® to slow down the leaks. Hi-Float® coats the inside of balloons with a special stretchy film with very small holes. It makes it harder for the helium molecules to leak through the walls of the balloons. Some will float for as long as 15 days! Now in gift shops they will often ask you if you want Hi-Float® used in your balloons. The shiny foil balloons made from Mylar® are also leak busters. Their surface has virtually no holes at all so they can stay filled for several weeks.


    Kathleen Carrado Gregar, PhD, Argonne National Labs 
    [email protected]
    April 1996


    Reference: WonderScience (American Chemical Society), November 1986.