system
Given the following post, respond as if you're commenting on Reddit:
human
Theoretically, what would stay cooler in the sun: a container that is pure white, or a container made of mirror?

Aren't both objects reflecting all light?
gpt
In an idealized case, no difference.  The only difference between a mirror and "white" is the *direction* that the light is reflected.  The amount of absorption is the same.

In practice, the mirrored one would stay cooler.  This is because practical whites are less reflective than high-quality mirrors; part of reflecting light in random directions is that sometimes they reflect light inward and absorb it.

Also, mirrored surfaces usually reflect non-visible wavelengths well.  White diffusers more commonly have a limited range of effective frequencies.