Flat glass composition comprising the following (expressed as percentages by weight): SiO2 60 75%; Al2O3 0 5%; Na2O 10 18%; K2O 0 5.5%; CaO 0 5%; MgO 0-2%; SO3 0 1%; Fe2O3 (total iron)>0.01%; TiO2 0-1% and one or both of: SrO 0-15%; BaO 0-15% with the proviso that the summed amount of SrO and BaO is greater than 4%. A preferred composition comprises: SiO2 65-74%; Al2O3 0-3%; Na2O 13 16%; K2O 0-2%; CaO 1-4.9%; MgO 0-2%; SO3 0-1%; Fe2O3 (total iron)>0.01%; TiO2 0 1%; BaO 4-10%; SrO 0-5%, wherein the summed amount of the alkaline earth metal constituents is in the range 10-13% and the summed amount of the alkali metal constituents is in the range 14-16%. The ferrous level of the glass may be greater than or equal to 28%, its performance in a thickness of 5 mm or less may be greater than or equal to 29 at LTA≧70%, and greater than or equal to 27 at LTA≧75%, and its liquidus temperature may be less than or equal to 980° C.