Packing Peanuts

    September 2016:

    Have you noticed that packing peanuts look different? Sometimes they are different colors (but that’s just because they add some color to the material in the peanut). The ones that are really different exist because they are made out of two very different materials. The original peanuts were made out of polystyrene. Polystyrene, or styrofoam, is a polymer, a molecule made up of lots of smaller styrene molecules. Styrene is made from petroleum oil meaning that it is made from carbon and hydrogen atoms. The newer peanuts are made from starch and consist of atoms of carbon, hydrogen, and oxygen. Starch is also a polymer made up of many glucose, or simple sugar, molecules. How can we tell the difference between these two?

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


    • Packing peanuts (styrofoam and starch) – a styrofoam egg carton will also work
    • A cup of water
    • A ¼ cup of fingernail polish remover (in a nonplastic container)
      • If you don’t have fingernail polish remover, gasoline will also work. You may want to use the fingernail polish remover or gasoline outside where the fumes are not confined to inside the house. Have an adult help you with this part of the experiment.
    • Aluminum foil

    Look closely at the peanuts and see the difference between them. You will notice that the styrofoam is a smooth peanut while the starch peanut is rougher on the edges. There is a more fun way to see the differences however. Place the peanut in some water. The styrofoam peanut will float and not interact with the water at all whereas the starch peanut will float but will also slowly begin to dissolve and get all sticky. This is because the oxygen and the hydrogen in the starch form interactions with the water molecules called Hydrogen Bonds. These interactions are strong enough that the water really likes to surround the starch molecule which is the beginning of dissolving the starch. On the other hand, water really doesn’t like to surround carbon-hydrogen bonds and so it repels the styrofoam peanuts. Now try the peanut in some fingernail polish remover. You will notice that the styrofoam peanuts really like to be surrounded by the acetone molecules in the fingernail polish remover, much more so than the starch peanuts. Look closely and you will see bubbles escaping the styrofoam peanuts as the peanuts melt into the acetone. The bubbles arise from the trapped air in the peanuts and is what makes them so good for packing. The air makes the peanuts very light and squishy so that they can absorb the shock when a package is dropped. It is amazing how many of the Styrofoam peanuts will go into the small amount of fingernail polish remover.

    If you pour off the liquid from the melted styrofoam and put the melted styrofoam on some aluminum foil and allow it to dry you will notice that the polymer changes the way it feels – allow the liquid to evaporate outside. It is now a hard plastic more similar to other polystyrene polymers like CD cases and plastic tableware. Other polystyrene polymers have a recycling code number “6”.

    If you are interested in the environmental aspects of the peanuts and are looking to compost or recycle them, please visit and see the short article on Packing Peanuts.