A complex film containing at least one functional material making it possible to modify the optical properties of the film between a first, transparent state and a second, reflecting state is deposited on at least some of the interior fittings of the passenger compartment of a motor-vehicle, which makes it possible to isolate the fittings covered over with the film from solar radiation in hot weather. The change of state is controlled electrically. The film can preferably be put into a third, opaque state, which makes it possible to accentuate the heating-up of the fittings under the effect of solar radiation in cold weather.