Are sun shades supposed to go on the outside of a car?

Car sunshades are usually recommended to be installed outside the vehicle, as this placement method more effectively blocks direct sunlight and lowers the interior temperature. With the sunshade positioned externally, its thermal insulation layer directly absorbs solar heat, minimizing heat transfer through the glass while simultaneously blocking UV rays to protect both interior items and occupants' skin. Conversely, when installed inside, some sunlight first penetrates the glass and reflects back into the cabin, diminishing the insulation effect. Common sunshade varieties include suction-mounted aluminum foil shades and magnetic no-trace fabric shades. The former secures to windows via suction cups, while the latter employs magnetic adhesion-both designs maintain clear driving visibility and feature simple installation. Additionally, pre-installation glass cleaning ensures secure adhesion, and prompt deployment when parked significantly reduces interior heat buildup, enhancing subsequent travel comfort.