Grades K–2 · Materials & Matter
How can a paper towel soak up water?
A puddle can disappear under a paper towel even when no one pours it away. The water has moved into the towel. A sheet that looks almost flat is really a tangle of tiny threads called fibers, with spaces between them.
Water is attracted to these fibers. When the towel touches a puddle, water enters the small spaces and spreads to nearby ones. That is why a wet patch can grow beyond the place that first touched the water. The towel does not need a little pump inside it.
The whole towel and its enlarged fibers connect the growing wet patch to the tiny spaces that hold the water.
The water is still there, held among the fibers. A wet towel feels different and weighs more because it now holds water as well as paper. When its available spaces become full, it cannot keep taking in more and more of a spill.
Not every sheet works this way. A wax coating can keep water from reaching the fibers underneath. The hidden spaces and the way water meets the material help explain why one sheet cleans up a spill while another helps keep a sandwich dry.
About this explanation
The fibers and spaces are drawn much larger than they really are. Different paper towels and coatings can take in different amounts of water.
Starting knowledge: Recognize a paper towel, liquid water and a difference between inside and on top.
Sources
- American Chemical Society — Designing an Absorbency Test