Deltas, home to over 600 million people globally, are on the front line of climate change. Deltas are facing intensified urban heat island (UHI) effects and altered hydrological regimes that do drive increased pluvial flooding. These microclimatic shifts—elevated ambient temperatures which affect prolonged heat stress, and disruptive surface runoff, directly threaten human health, infrastructure integrity, and ecological stability. This chapter argues for the transformative potential of advanced material science in the passive regulation of the urban microclimate itself, offering a pathway towards more resilient and livable deltaic communities. Our main objective in this chapter is to demonstrate how a materials framework can directly intervene in key local climate parameters, providing a crucial tool for designing sustainable urban environments in the world’s most vulnerable delta regions. The focus is on two synergistic, material-based strategies designed to directly alter the urban energy and water balance. The first explores cooling materials, including high-reflectance “cool roofs,” reflective paints, and phase-change materials (PCMs) integrated into building envelopes. These innovations are examined for their capacity to minimize solar heat gain, dissipate excess heat, and stabilize indoor temperatures, thereby mitigating the UHI effect and reducing cooling energy demand. The second critical area is the engineering of pervious and green infrastructure materials, such as permeable pavements and specialized substrates for bioswales and rain gardens. This category is analyzed for its dual function: managing the micro-hydrological regime by enhancing infiltration, retention, and evaporative cooling, while simultaneously reducing thermal mass and surface runoff that exacerbates flooding. By integrating these material science innovations, deltaic cities can achieve significant progress in passively managing their microclimates. This chapter provides a comprehensive overview of these materials, evaluating their efficacy, sustainability, and implementation challenges. The central objective is to demonstrate how a material-centric framework enables a direct intervention in core microclimate parameters, providing a critical tool for designing sustainable urban environments in the world’s most vulnerable deltaic regions.