There are three different kinds of polymers used for kitchen plastic wrap: Polyethylene (e.g., Handiwrap or Glad Wrap), polyvinyl chloride (e.g., Reynold's Plastic Wrap) and polyvinylidene chloride (e.g., Saran Wrap, which is almost 90% polyvinylidene chloride). Which of these materials is least permeable to water vapor? Or, in other words, which of these materials will best prevent evaporation? Do background research on these different polymer types in order to develop a hypothesis. Get samples of each type of plastic wrap, and use them to cover at least 9 identical drinking glasses (3 glasses for each wrap), each half-filled with water. Use a scissors to cut the plastic wrap, so it doesn't get stretched. Carefully seal the wrap on top of each glass with a rubber band. Label the glasses so you know which type of plastic wrap is used on each. Mark the water level on each glass. Keep the glasses together, so they are exposed to the same conditions. Check and record the water level in the glasses at regular intervals. It may take a few weeks, but keep checking until you can prove either that there is or is not a difference in the rate of water loss between the different types of polymers. Do you think you would get the same results at a different temperature (say, in the refrigerator)? Can you think of other ways you might test the permeability of plastic wraps to water vapor? (Goodstein, 2004, 65–69)
