How a Sheet of Paper Decides to Wrinkle or Fold
A thin rubber film lies on a table. Someone grabs it by the middle and slowly pulls upward. The film doesn't just rise: it arches into a dome, then wrinkles run along the dome's edge, like pleats on a skirt. Pull higher — the wrinkles gather into large folds that cross the entire film. And if you start lowering it, the folds don't disappear but collapse into new shapes.