Key concepts
Absorption
Paper
Water
Molecules

Introduction
We all know that washing hands throughout the day can help keep colds and flu at bay. So several times a day we lather up, scrub, rinse and then use a paper towel—then another one, maybe even three or four to dry them off. Because who wants wet hands?

But could there be a way to conserve some of that paper by getting a paper towel to go the extra mile, allowing you to dry your hands with just one single sheet? This activity just might help you find the answer.

Background
To understand how paper towels absorb water, we need to know a little about how they are made.

Paper towels are made of ground-up plant material. If you look through a microscope at a torn-up piece of paper (or look up some images on the Internet), you will see a web of tiny plant fibers. Magnifying your paper further will reveal that the fibers are made of long chains of linked sugar molecules, called cellulose. Water is attracted to cellulose and likes to be soaked up and stick to the cellulose in paper.

When you looked through your microscope, did you also see the spaces between the fibers? These empty spaces affect the absorbency of the paper: Water likes to stick together and fill these spaces as it follows the water attracted to the cellulose. More spaces allow more water to be absorbed. But what would happen if you add a tiny space between sheets of paper towels? Would the empty space between the sheets help to hold more water?

Materials

  • Five or more identical paper towels—preferably the type in public restrooms (In case you would like to test different types of paper towels, choose at least five identical towels of each type. Do not worry about wasting a few towels—this activity might help save paper in the long run!)
  • Water
  • Place to hang a paper towel to drip
  • Kitchen scale, one-gram precision or better
  • Paper and pen or pencil (for recording weights)
  • A workspace that can get a little wet
  • Scissors to make towels smaller for small hands (optional)

Preparation

  • Assemble all of your materials at your workspace.

Procedure

  • Unfold the first paper towel (if you have the prefolded type). Wet it thoroughly and hang it so all of the excess water drips out.
  • When the towel no longer drips, weigh it on a kitchen scale. You can heap up the towel on the scale rather than neatly folding it. Record the mass on a piece of paper.
  • Fold an identical paper towel in three (if it was not already prefolded) and fold it one more time so six layers of towel are on top of one another. Wet it thoroughly and hang it—still folded—so all of the excess water drips out. Do you think this folded paper towel holds more, less or just as much water as the unfolded paper towel?
  • When the folded towel stops dripping, weigh it on a kitchen scale. Do not unfold it; place it on the scale then read and record its mass. Does it weigh more, less or exactly the same as the wet unfolded paper towel? If there is a difference, why do you think the mass is different?
  • Now that you measured how much water the folded and unfolded paper towels can hold, and maybe found a difference, which do you think would dry your hands better?
  • Place a fresh, unfolded paper towel and an identical fresh paper towel folded in three in a dry spot on your workspace.
  • Wet your hands, shake them three times to remove most of the water and then dry them off with the unfolded paper towel. Do your hands feel completely dry, somewhat dry or still quite wet?
  • Repeat wetting and shaking your hands. Try to shake your hands in the same way you did the first time then dry them with the folded paper towel. How do your hands feel now? Do they feel dryer, wetter or just as dry as when you used the unfolded paper towel?
  • If your hands feel very dry with both the folded and unfolded paper towels, try again with half a paper towel, as follows: Cut a paper towel in half and dry your hands with an unfolded half-towel and with a folded half-towel. Do you feel a difference now?
  • How can your findings help you use fewer paper towels for the same job?
  • Extra: If you have more paper towels of the same type, repeat the tests; perform each step exactly the same way and notice the variations in the outcomes. Does the measured difference in mass vary a lot or just a bit? Is it always the folded or always the unfolded paper towel that weighs more? Do your hands always feel drier when using the folded or the unfolded paper towel? Scientists repeat tests to verify the outcome. Scientists also like to have their studies repeated by a different researcher utilizing different instrumentation (such as the scale). If the independent tests reveal the same results, the test is called reproducible. Such repeated tests by other experimenters have more scientific value. Can you find a friend to help you make your tests reproducible?
  • Extra: If you have different types of paper towels available, repeat the tests with them. Do you expect similar results? What did you find after testing them all?
  • Extra: Test other paper products that are used to absorb liquids, such as kitchen paper towels, toilet paper, paper napkins or tissues. Do these absorb more water when folded than when used single-layered? Which type of paper product gains most by folding? Can you explain why?

Observations and results
Did you measure a higher mass for the folded wet paper towel and did your hands feel drier when you used it? This is expected, as the tiny space between paper towel layers helps hold more water.

Paper is made of cellulose, which water molecules like to cling to. As a result, paper readily absorbs water. Paper towels are especially absorbent because their cellulose fibers have empty spaces—tiny air bubbles—between them. Water molecules, which like to stay together, follow the one another as they are absorbed by the cellulose and fill the empty spaces. Layering the paper towel creates more spaces for water to fill, which explains why your layered paper towel could hold more water and was more efficient at drying your hands.

The next time you reach for the paper towels, remember to fold! You might feel good knowing you just saved an extra paper towel from being used.

Cleanup
Let your wet paper towels dry, then recycle them if possible.

This activity was inspired by the TEDx talk, "How to Use One Paper Towel," by Joe Smith.

More to explore
How Do Paper Towels Absorb Water? from A Moment of Science, Indiana Public Media
How to Use One Paper Towel, from Joe Smith, TEDxConcordiaUPortland
Paper Chromatography, from Flashbang Science
Chromatography: Be a Color Detective, from Scientific American

This activity brought to you in partnership with Science Buddies

Science Buddies