Embodiments of radiant barriers for vehicles are disclosed. According to one embodiment, a vehicle includes an interior cabin at least partially enclosed by a roof panel, a floor panel, and an engine compartment firewall, and a radiant barrier positioned within the interior cabin. The radiant barrier includes a first thermally reflective surface and a second thermally reflective surface opposite the first thermally reflective surface and separated from the first thermally reflective surface by a thickness t. The thickness t is constant along a length and a width of the radiant barrier. The radiant barrier at least partially thermally isolates the interior cabin from an external environment.