Flat paper stained with water buckles and wrinkles as it swells and deforms out
of the original plane. Here we quantify the geometry and mechanics of a strip of
paper that swells when it imbibes water from a narrow capillary. Characterizing the
hygroexpansive nature of paper shows that thickness-wise swelling is much faster
than in-plane water imbibition, leading to a simple picture for the process by which
the strip of paper bends out of the plane. We model the out-of-plane deformation
using a quasi-static theory and show that our results are consistent with quantitative
experiments. C