A coated sheet-like plastics material comprising a) as base, a thermoplastic substrate; and b) on the base, a photocatalytically active coating comprising a water-spreading layer which involves either a sol-adhesion-promoter layer, layer b1+2), comprising an adhesion promoter and a colloid sol, or a colloid-sol layer b2) arranged on an adhesion-promoter layer b1) applied on the substrate a), and a photocatalytically active layer b3) arranged on the water-spreading layer b1+2) or b2), where b3) is obtainable through application and drying of a mixture comprising, based on the solids content of the mixture in percent by weight b31) from 1 to 25% of titanium dioxide and b32) from 75 to 99% of silicon dioxide and/or of a metal oxide which is not soluble in water or of an anionically modified silicon dioxide or metal oxide; where the titanium dioxide is particulate with an average primary-particle size smaller than 10 nm. In-line process for producing said material, and also use as roofing material or as glazing material, preferably in areas with moist conditions. The coated sheet-like plastics material of the invention combines water-spreading properties with photocatalytic activity, without any damage to the thermoplastic substrates. The coated sheet-like plastics substrate of the invention is produced in a relatively uncomplicated, inexpensive and fast in-line process and, in use, provides impressive substrate stability and impressive effectiveness of the coating in resisting initial algal growth.