angle measurements for four combinations of wax and LIG-E channels. Neat paper and LIG-E absorb a water droplet within <50 ms, whereas waxed cellulose and LIG-E exhibit static hydrophobicity with high contact angles. Scale bar: 500 μm. A lateral capillary-driven flow (b) is evaluated by monitoring the waterfront as a function of time (c) across a strip of neat paper, LIG-E, and oxygen plasma-treated LIG-E. The shaded areas correspond to fits to the Washburn equation including standard deviations, which allow us to extract the Washburn diffusion coefficients (d). Similarly, in a vertical flow configuration (e), we characterized the front positions (f) and extracted their Washburn diffusion coefficients (g). The grey zones in panels (c) and (f) represent the duration of flow across the materials. Interestingly, while wicking through lateral channel networks has been extensively studied , the vertical flow dynamics across multilayers structures in an out-of-plane direction have never been explored, despite their applications in many commercial diagnostic devices . Surprisingly, we found that vertical flows exhibit Washburn diffusion coefficients approximately 5-fold lower than their lateral counterparts (Fig. ), despite significantly shorter timescales and smaller diffusion distances. We hypothesize that the slower wicking observed in vertical configurations is due to the in-plane fiber direction and non-ideal contact between cellulose layers.