That's what I was thinking of. They laminated a reflective material under a thin sheet that had a particular absorption spectrum, with a thermally conductive bond, and put fused silica on top of it to protect against weather.
Laser-etching of normally reflective metals makes the material less complex. For one, you don't have to match thermal expansion coefficients any more.
The night-sky radiative cooling concept is thousands of years old-- https://en.wikipedia.org/wiki/Yakhchal --but we have better materials now. India and Persia made ice by filling shallow trays with water, insulating them underneath with straw, and exposing the water to a calm, clear, night sky.
Laser-etching of normally reflective metals makes the material less complex. For one, you don't have to match thermal expansion coefficients any more.
The night-sky radiative cooling concept is thousands of years old-- https://en.wikipedia.org/wiki/Yakhchal --but we have better materials now. India and Persia made ice by filling shallow trays with water, insulating them underneath with straw, and exposing the water to a calm, clear, night sky.