You cannot fold a piece of paper more than seven times

What actually happened

The classroom demonstration works because everyone uses a letter-sized sheet. Each fold doubles the thickness and halves the usable length, and standard paper runs out of length before the eighth fold. That is a fact about the sheet in your hand, not about the universe.

Gallivan, then a junior in high school in California, took the challenge as extra credit. She derived a formula relating the number of folds to the required paper length and thickness, showing that folding in a single direction requires length L = (πt/6)(2ⁿ + 4)(2ⁿ − 1) where t is thickness and n the number of folds. Then she bought a 1,200-meter roll of toilet paper, laid it out in a shopping mall corridor, and folded it twelve times in a single direction. She published her work in 2002. The record has since been pushed further by other groups using longer materials, including a run by MIT students using industrial toilet paper in a hallway.