A surfactant-free acetate-triethanolamine two-step catalytic sol-gel process with varying solvent content prepared marshmallow-like macroporous silicone monoliths. The resulting gels had fewer bubbles and other defects than conventional preparation methods. These materials exhibited high total reflectance of over 95.0 % in the visible light region. Samples with optimized solvent-to-precursor ratios show absolute reflectance greater than 97.5 % at 400 nm-1100 nm and can be used in place of reflectance standards. Unlike existing reflectors, macroporous silicon monoliths are bulk materials that can be fabricated in a single reaction, allowing them to be large-area and arbitrarily shaped. These materials can be used not only for indoor measurements but also for outdoor telemetry applications such as drones and robots. They also exhibit excellent solar reflectance and significant absorption suppression over the entire wavelength range of sunlight. Their water repellency, UV resistance, low thermal conductivity, and efficient radiative cooling properties make them an ideal material for outdoor thermal management. The results of this study suggest that macroporous silicon monoliths have potential for use as a highly solar-reflective material that can successfully control surface temperature rise while contributing to environmental concerns.