A coated substrate including: a substrate including a treated layer, a photocatalytic layer, and a protective layer between the photocatalytic layer and the treated layer, the protective layer comprising colloidal particles dispersed in a matrix, the colloidal particles including first and second types of particles that differ in their respective particle size distributions and which together provide a physical barrier by virtue of the first, smaller particles at least partially filling interstices between the second, larger particles and thereby impede photocatalyst derived degradation of the treated layer, the first type of colloid particles comprising hydrolyzed silica based material such as reactive silica condensate particles or polyhedral oligomeric silsesquioxanes, or mixtures thereof, the protective layer having an effect of less than 20 delta E units on the color and gloss of the substrate.