Scientific American magazine (Aug 2021) has a short piece about a new nanomaterial mixture, now as paint, that lets surfaces release more heat than they absorb. This technique has been used for experimental cooling devices, though not in commercial use yet.
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This coating absorbs just 1.9 percent of sunlight compared with 10 to 20 percent for conventional white or “heat-reflective” paints, says Purdue University mechanical engineer Xiulin Ruan, co-author of a study on the substance in ACS Applied Materials & Interfaces.
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In the past 10 years researchers have found greater success with multilayered coatings that incorporate tiny particles of varying sizes, some on the nanoscale, to reflect many wavelengths of light. Teams at Stanford University and the University of Colorado Boulder have shown that such materials can cool a surface to below the ambient temperature.
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The reflectivity of shiny aluminium is reported by Reynolds as 88%
But this chart from The IESNA Lighting Handbook:
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Mirrored and optical coated glass 80-99 (mirroring is silver on polished glass)
Metallized and optical coated plastic 75-97 (generally vacuum deposited aluminum)
Processed anodized and optical coated aluminum 75-95 (what passes for chrome on cars now)
Polished aluminum 60-70
Chromium 60-65
Stainless steel 55-65
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And each material has slightly different emissivity.
-mort