Is the radiative cooler really just an aluminum disc painted black? Why this material versus some of the other designs out there (some groups have made these out of wood, others with glass microspheres in polypropylene, etc)
The fancier materials work is for two things: 1) selective emission which can allow the radiative cooler to get to a colder temperature than a natural material (many/most of which have relatively uniform emissivity), and 2) high solar reflectance at the same time, which can allow radiative cooling during the day as well.
A dual-mode textile for human body radiative heating and cooling[3]
[1] https://web.stanford.edu/group/fan/ [2] https://web.stanford.edu/group/fan/publication/Goldstein_Nat... [3] https://web.stanford.edu/group/fan/publication/Hsu_ScienceAd...