This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Look closely at Hokusai's The Great Wave off Kanagawa, one of Japan's most iconic masterpieces. The brilliant white of the waves, snow on Mount Fuji and clouds above contain no white pigment.
Instead, their whiteness comes from the way light scatters off the unprinted fibers of the washi paper itself. This optical phenomenon—known as structural whiteness—is the same mechanism that makes sea spray, snow and clouds appear bright white in nature. Throughout nature, from plant tissues to protective frog nests, foamed structures made mostly of air scatter light with extraordinary efficiency, creating intense whiteness without the need for pigments.
This natural phenomenon inspired an international research team—led by Professor Easan Sivaniah of Kyoto University's Institute for Integrated Cell-Material Sciences (iCeMS), alongside collaborators from Tokyo Metropolitan University and Donghua University—to develop a new foam-based materials platform that solves two major industrial challenges in everyday materials. Their work is published in the journal Nature. Today, white packaging, films and coatings rely heavily on titanium dioxide (TiO₂) to provide brightness and opacity in creating white materials, but safety concerns recently led the European Union to ban its use as a food additive.
Meanwhile, fluorinated materials known as PFAS are widely used to provide water and oil repellency, but growing concerns about their persistence and potential environmental and health impacts are driving efforts around the world to develop alternatives. To address these challenges, the team developed a technology that generates whiteness and controls water repellency through precisely engineered porous structures that reproduce the light-scattering behavior of natural foams, drawing inspiration from natural surfaces such as leaves and flower petals. "A key challenge faced by biomimetic science is realizing environmentally friendly material designs inspired by nature at the scale and cost of existing materials," said Associate Professor Taiki Yanagishima, Tokyo Metropolitan University The fabrication process is remarkably simple.
It uses light followed by treatment with a mild solvent. Light first breaks the polymer into smaller molecular fragments. These fragments interact with the solvent, causing the material to swell and form an open, porous structure.
Through this single process, the material achieves two distinct functions. Internally, the porous structure scatters light to create intense whiteness without added pigments. On the surface, the foam transforms into an extremely rough structure with strong water-repellent properties, similar to those found on a lotus leaf.
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