The quest to identify the whitest thing on Earth moves beyond simple observation, focusing instead on a precise scientific measurement of light interaction. Whiteness is a demonstration of maximum light scattering and reflection across the entire visible spectrum. A truly white material scatters all wavelengths of incoming light equally and efficiently, allowing virtually none of the light to be absorbed. This capacity for total, non-selective light reflection is the defining characteristic.
The Science of Extreme Reflectance
Achieving extreme whiteness requires a material to maximize diffuse reflection while minimizing absorption. Light hitting a smooth surface produces specular reflection, where the light rays bounce off at a single, mirrored angle. In contrast, a white surface utilizes diffuse reflection, where light rays scatter in many directions due to microscopic surface roughness or internal structure.
The standard for measuring whiteness is Total Hemispherical Reflectance (THR), which quantifies the total fraction of light reflected. A high THR value indicates a material’s broad efficiency in reflecting light across the visible and often the near-infrared spectrum. To achieve this broadband reflection, the material must contain particles with a high refractive index contrast and be distributed across a range of sizes.
The Current Whitest Material on Earth
Material Composition
The current record-holder for the whitest material is an ultra-white paint developed by engineers at Purdue University. This engineered coating achieves a remarkable solar reflectance of 98.1%, setting the benchmark for whiteness. The paint’s extreme reflectivity is due to its high concentration of barium sulfate (\(\text{BaSO}_4\)) particles, a compound also used to make photo paper and cosmetics white. It surpasses previous standards like Magnesium Oxide or polytetrafluoroethylene (PTFE) by maximizing the scientific principles of light scattering. The material’s design features a high volume concentration of barium sulfate, which is approximately 60% of the paint’s total formulation.
Passive Radiative Cooling
The paint’s whiteness is so intense that it also reflects infrared heat, enabling passive radiative cooling. This property means that a surface coated with the material actively rejects heat, cooling the surface to below the ambient air temperature. In field tests, surfaces coated with the paint have been measured to be more than \(4.5^\circ\text{C}\) cooler than the surrounding air under peak sunlight. Applied to a \(1,000\) square foot roof, this cooling effect can provide a cooling power of up to 10 kilowatts, which is comparable to the central air conditioning unit used in many homes.
Nature’s Most Brilliant White Surfaces
While engineering has produced the whitest paint, nature offers some of the most visually brilliant white surfaces through specialized structures. Fresh snow is an excellent example of a highly reflective natural material, with a solar albedo that can exceed \(85\%\). The whiteness of snow does not come from a pigment but from the complex structure of countless ice crystals and the air gaps between them. Light is repeatedly scattered and reflected at the numerous ice-air interfaces, ensuring all visible wavelengths are returned to the eye.
Biological systems also produce impressive whiteness, such as the scales of the Cyphochilus beetle, native to Southeast Asia. This beetle’s scales are whiter than paper, a feat achieved not with pigment but with a thin, disordered network of chitin filaments. This intricate, foam-like photonic structure is optimized to scatter light efficiently, maximizing whiteness with a minimal amount of material. Although visually striking, these natural surfaces still have limitations in total reflectivity compared to the engineered paint, often due to structural irregularities or absorption bands.