Why are astronaut spacesuits white?

In a vacuum, there is no air and no wind to carry heat away: it can only arrive and leave by radiation. A suit exposed to the Sun without an atmospheric filter receives a considerable flux, while the same surface, moved into Earth's shadow, cools abruptly. A light-colored outer layer reflects most visible light while still radiating infrared well: it limits heating without preventing the suit from shedding its own heat. Beneath this fabric, layers of metallized insulating film do the rest, and a garment lined with chilled water draws heat away from the body, the main source of overheating during exertion.

The second reason is operational. Against the black background of space or dark continents, a white silhouette is spotted immediately, both through windows and on camera footage. Since two identical suits are indistinguishable, colored stripes have been added to the legs and arms to tell crewmates apart, a practice inherited from the lunar missions, where the commander wore red markings.

Garments worn inside a spacecraft don't follow the same specifications: they serve as a backup in case of depressurization, without direct Sun exposure or independent cooling. Their color therefore follows other criteria: visibility at sea and for rescue teams in the case of orange suits, branding for the dark outfits of commercial spacecraft. Future lunar suits, for their part, will keep a white outer shell, for the same thermal reason.