Why does a paper towel soak up a spill so quickly?
Show answer & explanation
Answer: Water creeps into the narrow gaps between its cellulose fibres by capillary action
It is coated with a chemical that attracts water — Wrong. Ordinary paper towels carry no water-attracting coating; extra treatment would, if anything, slow absorption. Cellulose attracts water on its own, and the embossed patterns some brands add simply create more open space for capillary action to fill.
The sheet forms a small vacuum that sucks the liquid in — Wrong. Nothing in a paper towel pumps air out or creates suction; a towel lying on a counter is open to the air on every side. The liquid moves because it wets the fibres and is pulled along the narrow spaces between them, not because a pressure difference sucks it in.
Water creeps into the narrow gaps between its cellulose fibres by capillary action ✓ — Correct! A paper towel is a loose mat of cellulose fibres with countless narrow gaps between them. Water clings to cellulose and water molecules cling to each other, so the liquid is drawn into those gaps and spreads through the sheet, even upward against gravity. That is capillary action, the same effect that lifts water up a plant stem.