Mystery #2Tier 2water / capillary action

Why does water climb up a paper towel?

Dip just the corner of a paper towel into water and the wetness creeps upward, climbing against gravity all by itself. Nothing is squeezing or pulling it. What makes water climb?

Ink-dyed water creeping upward through a strip of paper, carrying colours with it, the same capillary wicking that draws water up a paper towel. — Photo: Oscar, Wikimedia Commons · CC BY-SA 3.0 · via Wikimedia Commons

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