Key Concepts
Absorption, paper, adhesion, cohesion
Someone wiping their hands with an unfolded paper towel

Introduction

It’s fall, which means flu season. We all know that washing hands a few extra times a day can help keep colds and flu at bay, so we wash hands frequently and use a paper towel…then another one, maybe even three or four to dry them off. Because who likes to go out with wet hands in cold fall weather, right?

But could there be a way to conserve some of that paper, and get 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.

This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.

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 microscopic plant fibers. Magnifying your paper even more, you would see that the fibers are made of long chains of linked sugar molecules, called cellulose. Water is attracted to cellulose, so water molecules like to be soaked up and stick to the cellulose in paper.

As 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 up 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 available in public restrooms. In case you like to test different types of paper towels, at least five identical towels of each type. (Do not worry about wasting a few towels now, 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.

Preparation

  1. Choose a workspace that can get a little wet.

Procedure

  1. You will do an objective test (weighing the wet paper towels) before you perform a subjective test (how dry your hands feel when using the paper towels).
  2. Unfold the paper towel, if you have the pre-folded type. Wet it thoroughly and hang it so all of the excess water drips out.
  3. When the towel no longer drips, weigh it on a kitchen scale. Just heap up the towel on the scale, do not neatly fold it. Mentally record the mass or write it down on a piece of paper.
  4. Fold an identical paper towel in three (if it was not already pre-folded) and fold it one more time so six layers of towel are on top of each other. 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?
  5. When the folded towel stops dripping, weigh it on a kitchen scale. Do not unfold the towel, put it on the scale and read 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?
  6. Now that you measured how much water the folded and unfolded paper towel can hold, and maybe found a difference, do you think the unfolded or the folded towel would dry your hands better?
  7. Place an unfolded paper towel and an identical paper towel folded in three in a dry spot on your workspace. We advise that you cut the paper towels in half for child-sized hands.
  8. Wet your hands, remove most water by shaking them three times and then dry them off with the unfolded paper towel. Do your hands feel completely dry, somewhat dry or still quite wet?
  9. Repeat the wetting and shaking of your hands. Try to shake your hands in the same way you did the first time and dry off your hands 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?
  10. 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?

Extra: If you have more paper towels of the same type, repeat the tests, performing each step in 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? How about your feeling: 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 a different instrument (like a different scale). If the independent test reveals the same results, the test is called reproducible. Reproducible tests 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?

Extra: Test other paper products that are used to absorb liquids, like 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 a folded paper towel?  This is expected, as the tiny empty space between layers of paper towels helps hold more water.

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

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 without sacrificing comfort!

Cleanup

  1. Let your wet paper towels dry and put them in the recycle bin.

More to Explore

Credits

Sabine De Brabandere, PhD, Science Buddies

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Key Concepts
Absorption, paper, adhesion, cohesion
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