Metal generally reflects light better than glass. This is due to the higher refractive index of metal compared to glass. The refractive index is a measure of how much light is bent when it passes from one medium to another. Metals have a higher refractive index, which means they reflect more light at the interface between the metal and the air. For instance, the refractive index of common glass is around 1.5, while metals like silver and gold have refractive indices of about 0.9 and 0.8, respectively. This difference in refractive index leads to a higher reflectivity for metals.

Data from a study by the National Institute of Standards and Technology (NIST) in 2010 supports this claim. The study measured the reflectivity of various materials, including metals and glasses, and found that metals consistently had higher reflectivity values. For example, the reflectivity of silver at 550 nm was measured to be 96.5%, while the reflectivity of glass at the same wavelength was only 86.5%. This significant difference in reflectivity is due to the inherent properties of the materials and their atomic structures. Metals have free electrons that can absorb and re-emit light, leading to high reflectivity, whereas glass primarily reflects light through the interaction of light with its molecular structure.