Various disperse dyes on cellulose triacetate film and some on cellophane (regenerated cellulose film) sealed in envelopes of undyed hydrophobic films, polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), poly (ethylene terephthalate) (PETP), and cellulose triacetate (CT) have been exposed to light from a 400 W mercury lamp. Fading is retarded by the undyed fibers in the following orders of effectiveness -- PTFE, PAN, PETP, CT. The permeability of water vapor (except for polyacrylonitrile) or oxygen through these films decreases in the same order. The retardation is similar in magnitude to the corresponding differences in light fastness of the disperse dyes on textile fibers. It is suggested that the action is caused by retardation of the diffusion of an oxygen molecule towards contact with a dye molecule during the short lifetime of the excited state of the dye, calculation showing that there is only a very small chance of such contact. An expression is derived which shows the rate of diffusion of oxygen in the substrate. The retardation effect termed diffusion restriction (DR) probably operates to some extent in all fading of colorants in fibers or films and may explain the increased fading at high humidity when the dye fibers are smaller and the dye molecules are more accessible, giving lower DR and lower light fastness. The reduction in fading due to this process is not very large, less than one unit on the blue wool scale. This work casts an interesting light on the possibilities of surrounding art objects with inert gas to prevent fading due to the presence of oxygen but the reduction in fading may not be sufficient to be worth the effort involved. -- AATA