A transfer foil comprising a carrier sheet and a thermally transferable overlay, the overlay comprising a transparent film of polymeric material having dispersed therein surface-stabiiised titanium dioxide, wherein the titanium dioxide is stabilised by coating the surface with alumina, silica or zirconia or mixtures thereof. A thermal transfer dye sheet ribbon comprising a substrate supporting different coloured dyecoats provided as discrete uniform print-size panels arranged in a repeated sequence along the ribbon, and a thermally transferable overlay comprising a transparent film of polymeric material having dispersed therein surface-stabilised titanium dioxide, positioned between each repeated sequence of the dyecoat panels, wherein the titanium dioxide is stabilised by coating the surface with alumina, silica or zirconia or mixtures thereof.