Paper Towel Absorbency Experiment: Do It Like a Lab

Every paper towel advert makes the same comparison and every one of them is rigged: a bigger sheet soaks up more water, so whoever sells the bigger sheet wins. A paper towel absorbency experiment done properly asks a different question. Not how much water does one sheet hold, but how much water does each gram of paper hold, and how fast does it get there. Those two answers often point at different brands, and when a nine-year-old discovers that the cheap towel wins on one measure and loses on the other, the argument about which is “better” suddenly needs a definition.

Key Takeaways

• You’ll weigh equal squares of three towels dry and wet to get absorbency per gram, then race wicking strips up out of a dish of coloured water.
• It teaches fair testing: controlling area, soak time and drip time so the only thing that differs is the towel.
• Best for ages 6–12. Six-year-olds can do the whole thing with help on the division.
• The usual mistake: comparing whole sheets, which measures sheet size rather than the paper.
• The wicking front slows down as it climbs, and it does so in a pattern you can predict.

What You’ll Need

Item	How much	Where to get it	If you don’t have it
Three different paper towels	3 sheets of each	Supermarket; borrow a sheet from a neighbour for a third brand	Kitchen roll, a cheap café napkin and a tea towel make a fine trio
Kitchen scale reading to 1 g	1	Supermarket, about the price of two coffees	The volume method in Step 7 needs no scale, but is rougher
Ruler and scissors	1 each	Kitchen drawer	Fold-and-tear along a crease
Shallow dish or saucer	2	Kitchen	A plate with a rim
Measuring jug, 250 mL	1	Kitchen	A marked baby bottle
Food colouring	A few drops	Baking cupboard	Strong tea, or a washable marker scribbled on the strip’s bottom edge
Pencil and tape	1 each	Kitchen drawer	Clothes pegs and a chopstick
Stopwatch	1	Phone	Any clock with a second hand
Paper for a results table	1 sheet	Anywhere	Nothing else needed
Tray or towel to work on	1	Kitchen	Do it outside or over the sink

Time: prep 10 min, experiment 35 min, cleanup 5 min Cost: everything is probably in your kitchen Mess level: medium. Water, dye and soggy paper. Work over a tray

Do the Experiment: A Paper Towel Absorbency Experiment, Two Ways

Step 1 — Cut three 10 cm squares from each towel

Measure and cut carefully. Equal area is the control that makes the whole thing valid, and a sloppy square is a hidden variable. Label each square’s brand in pencil on a corner, lightly.

Step 2 — Weigh every square dry and write it down

A single square of kitchen towel weighs somewhere between 1 and 4 g. If your scale only reads whole grams, weigh all three squares of a brand together and divide. Record the dry mass before anything gets wet, because afterwards you cannot go back.

Step 3 — Soak for exactly 30 seconds

Fill a dish with 1 cm of water. Lay a square flat on the surface, start the stopwatch, and let it sit untouched for 30 seconds. Do not press it, do not stir, and do not use warm water for one and cold for another.

Step 4 — Lift, drip for exactly 20 seconds, then weigh

Lift the square by one corner with tweezers or two fingers, hold it over the dish and count 20 seconds. The dripping stage is where most home versions fall apart, because “until it stops dripping” is not a time. Then put it straight on the scale.

Step 5 — Calculate absorbency per gram

Wet mass minus dry mass gives the water held, in grams. Divide that by the dry mass. The answer is a ratio, often somewhere between 4 and 10, meaning the towel holds four to ten times its own weight in water. That number, not the raw grams, is the one worth comparing.

Step 6 — Run the wicking race

Cut a 2 cm by 15 cm strip from each towel. Tape all three to a pencil, hang the pencil across two mugs so the strip ends sit 1 cm deep in a dish of dyed water, and start the clock. Mark the height of the wet front at 15, 30, 60, 120 and 240 seconds with a pencil tick.

Step 7 — Repeat everything twice more

Three squares and three strips per brand. Average them. Note the spread too, because if the spread between your own three squares is bigger than the gap between brands, you have not actually shown a difference.

What you should see: Most kitchen towels hold between four and ten times their dry weight in water, and the ranking by that ratio frequently disagrees with the ranking by raw grams per sheet. The quilted, embossed, expensive towels usually win on total grams and often lose on grams per gram, because much of their advantage is simply having more paper. In the wicking race the wet front climbs fast at first and then visibly stalls: expect something like 4 cm in the first 30 seconds and only another 2 cm in the following 90. One strip will usually climb higher than the others but not necessarily be the one that held the most water.

What’s Actually Going On

Water climbs into paper by capillary action. Paper is a tangle of cellulose fibres with gaps between them, and cellulose is hydrophilic, meaning water molecules are attracted to it more strongly than they are to each other. At the edge of the wet region, the water surface curves into the tiny gaps, and surface tension pulls the whole column along behind it. The US Geological Survey’s water science school page on capillary action describes the same effect in soil and in plant stems, which is where it matters most: it is how water gets from a root to a leaf.

The quantitative law was worked out by Edward Washburn in 1921 in Physical Review, in a paper called “The Dynamics of Capillary Flow”. The result, now called the Lucas–Washburn equation, is that the distance liquid penetrates a capillary grows as the square root of time. Double the distance and it takes four times as long. That is exactly the stalling your strips show. If your child plots height against the square root of time rather than against time, the curve straightens into a line, and that moment is worth more than the whole brand comparison.

The equation also says which towel wicks fastest. The rate rises with pore size, surface tension and how well water wets the fibre, and falls with viscosity. Big pores wick fast. But capillary rise height works the opposite way: narrow pores pull water further up against gravity. So a towel with wide channels will race up quickly and then stop lower, while a dense towel climbs slowly and keeps going. There is no single “most absorbent” structure, only trade-offs, and the engineering compendium Wicking in Porous Materials edited by Masoodi and Pillai spends a book on exactly that tension.

One more thing the advertising hides. Embossing, the quilted pattern pressed into premium towels, is not decoration. It creates voids between the plies that store bulk water, which raises total capacity without making the fibre itself any more absorbent. So two honest answers to “which towel is more absorbent?” exist, and they measure different things: capacity per gram measures the paper, capacity per sheet measures the product. Both are legitimate. Confusing them is how you get a misleading advert.

How to Explain It to Your Kid

Ages 5–8: paper is full of tiny tunnels

Show them the strip climbing and tell them the paper is full of tunnels too small to see, and that water likes the tunnel walls so much it crawls into them, dragging more water behind it. Then point out the stalling. Ask why the water does not just keep going all the way up. The honest answer at this age is that the water already up there is heavy, and the pull at the top has to lift all of it.

Ages 9–12: absorbency means water per gram of paper

Do the division with them. A towel that holds 15 g of water but weighs 3 g holds five times its weight. A towel that holds 18 g but weighs 4.5 g holds four times its weight. The second one soaked up more water and is the less absorbent paper. That distinction is the whole article in one sentence, and it is the kind of thing a child can genuinely explain to an adult.

Ages 13+: the square-root law, and why it is a law

Give them the Lucas–Washburn result and have them test it. Plot their five time points against the square root of time and look for a straight line. Then have them think about where it should fail: very early on, when the strip’s bottom edge is still flooding; and very late, when gravity stops being negligible. A model with a known range of validity is a much more grown-up idea than a model that always works.

The question to ask: “If I gave you a towel that climbs higher in the wicking race but holds less water per gram, which job would you give it: mopping a big spill off the floor, or drying between the slats of a dish rack?”

Why Teaching This Early Pays Off

This is the cheapest good fair test in the house. Almost every school science investigation a child will ever do has the same structure: hold everything constant except one thing, measure a number, repeat, and compare the spread within a group against the gap between groups. The National Research Council’s K-12 framework lists “planning and carrying out investigations” and “analysing and interpreting data” among the eight practices of science, and a paper towel test exercises both in under an hour with no equipment.

The specific payoff is the per-unit idea. Grams of water per gram of paper is the same mental move as price per 100 grams on a supermarket shelf, miles per gallon, cases per 100,000 people and goals per game. Children who do not have it read every comparison as a raw total, which is precisely what advertising and bad statistics rely on.

The structure in the “what you should see” section, where you ask for a prediction before the result appears, comes from White and Gunstone’s Probing Understanding and its Predict–Observe–Explain routine. Chi and Wylie’s ICAP framework gives the reason it works: a learner who commits to a prediction and then has to reconcile it with the evidence is doing more cognitive work than one who watches and agrees. Be honest about scale, though. One towel experiment does not make a scientist, and the research on hands-on learning is mostly about classroom-length interventions, not single afternoons. What it does reliably do is give you a concrete shared memory to point back to the next time your kid meets a comparison that smells unfair.

Before You Start: What Parents Should Know

Best age	6–12. Under 6, the timing and the equal-square cutting are the hard parts, not the idea
Supervision	Light. Scissors, and an adult to run the stopwatch for younger kids
Real hazards	None beyond normal kitchen care. Food colouring stains clothes and worktops, so use a tray
Don’t	Don’t squeeze or wring the wet squares before weighing. One squeeze and the comparison is over

When It Doesn’t Work

• All three towels give nearly identical numbers. That is a real result, and quite common within one price tier. Add a very different material to widen the range: a café napkin, a cotton tea towel, a sheet of newspaper.
• The scale reads 0 g for a dry square. Weigh three or five squares together and divide. Cheap scales round to the nearest gram, and a single sheet can be below their resolution.
• The strips curl out of the water or fall in. Tape them to the pencil with a slight tension and make sure only 1 cm is submerged. A strip that flops into the dish is wicking from its whole length and the race is void.
• The wet front is too blurry to mark. Add more food colouring, and mark the leading edge of the colour rather than the middle of the fuzzy band. Pick one rule and use it for all three strips.
• Everything drips for different lengths of time. It will, which is why the 20-second count exists. Use a stopwatch, not judgement.

Take It Further

1. Change one variable: water temperature. Run the whole test with cold water and again with warm, around 40 °C. Warm water has lower viscosity and lower surface tension, which pull the wicking rate in opposite directions, so predicting the result is genuinely hard. Measure it.
2. Change the liquid. Wick water, cooking oil and soapy water up strips of the same towel. Soapy water has much lower surface tension and climbs less far, which is a direct test of the Washburn equation’s surface-tension term.
3. Plot it properly. Take ten time points instead of five, then graph height against time and height against the square root of time on the same page. Having a child discover which graph is a straight line is a better statistics lesson than any worksheet.

Capillary action is the same mechanism that makes water walk between cups along a paper bridge, demonstrated in our walking water capillary action setup. For the opposite case, surfaces that refuse to let water in at all, see why raincoats work, and for the surface tension that does the pulling, try the surface tension experiment with needles and coins.

What to Watch For Over the Next 3 Months

• Week 4: They question an advert out loud. “But how big is their sheet?” is the sound of this working.
• Month 2: The per-unit move shows up in a shop, usually about sweets or crisps, as “that one’s more per gram”.
• Month 3: They propose a fair test unprompted for something unrelated: which glue is strongest, which route to school is faster, which crisp packet has the most air. Say yes, and make them name the thing they are holding constant.

Frequently Asked Questions

Do I really need a kitchen scale?

A scale makes this a real measurement, and one that reads to 1 g is enough. Without it, you can measure what is left: put 50 mL of water in a saucer, soak the square, and pour the remainder back into the jug. The missing millilitres are grams of water absorbed, roughly, but you lose the per-gram comparison that makes the test worthwhile.

Which paper towel actually wins?

It depends on the measure, and that is the lesson rather than a dodge. In most household trials premium quilted towels hold more water per sheet, while cheaper single-ply towels are competitive or better per gram of paper. Brands reformulate constantly, so trust your own numbers over anyone’s claim, including ours.

Can we use this for a school science fair project?

It is one of the better choices, because the data is quantitative and the controls are easy to defend. Judges respond well to three trials per sample, a stated spread, and a graph. The square-root plot from Step 6 will put the project ahead of most.

My six-year-old lost interest during the weighing. Is it still worth it?

Give them the stopwatch and the pencil ticks on the wicking strips. The climbing coloured front is the part that holds attention at that age, and the weighing can be yours. They will still get the main idea, which is that we kept everything the same except the towel.

Does it matter if the towel is a double sheet?

Yes, enormously, and it is the most common way to ruin the test. Use exactly one ply thickness of each product, or if a product only exists as a bonded two-ply, say so in your notes and compare on the per-gram basis, where ply count stops mattering.

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About the author

Ricky Flores is the founder of HiWave Makers and an electrical engineer with 15+ years of experience building consumer technology at Apple, Samsung, and Texas Instruments. He writes about how kids learn to build, think, and create in a tech-saturated world. Read more at hiwavemakers.com.

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Sources

1. Washburn, E. W. (1921). “The Dynamics of Capillary Flow.” Physical Review, 17(3), 273–283. https://doi.org/10.1103/PhysRev.17.273
2. U.S. Geological Survey, Water Science School. “Capillary Action and Water.” https://www.usgs.gov/special-topics/water-science-school/science/capillary-action-and-water
3. U.S. Geological Survey, Water Science School. “Surface Tension and Water.” https://www.usgs.gov/special-topics/water-science-school/science/surface-tension-and-water
4. Masoodi, R., & Pillai, K. M. (Eds.). (2012). Wicking in Porous Materials: Traditional and Modern Modeling Approaches. CRC Press. https://doi.org/10.1201/b12972
5. White, R. T., & Gunstone, R. F. (1992). Probing Understanding. Falmer Press, London.
6. Chi, M. T. H., & Wylie, R. (2014). “The ICAP Framework: Linking Cognitive Engagement to Active Learning Outcomes.” Educational Psychologist, 49(4), 219–243. https://doi.org/10.1080/00461520.2014.965823
7. National Research Council. (2012). A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas. National Academies Press. https://doi.org/10.17226/13165