Absorptivity is the measure of how much radiant heat a surface takes in. For cars, this directly affects engine bay cooling and cabin temperatures. A dark car body has high absorptivity, meaning it gets hot quickly under the sun, putting a heavier load on the A/C system.
In contrast, engine radiators are designed with low absorptivity for external radiant heat but high thermal conductivity. The raw aluminum fins release heat into the passing air rather than absorbing heat from the hot road or exhaust pipes.
Engineers use specialized coatings to control absorptivity. Ceramic coatings on headers lower their heat release. This keeps exhaust gas hot and moving fast, while protecting nearby wiring from heat damage.