A thermoplastic molding composition suitable for preparing articles by thermoforming is disclosed. The molding composition that comprise A) branched, aromatic poly(ester)carbonate, B) graft polymer, C) an optional vinyl(co)polymer and or polyalkylene terephthalate, D) at least one flame retarding phosphorous compound selected from the group consisting of mono- and oligomeric phosphorus and phosphonic acid esters, phosphonate amines and phosphazenes and E) talc, is characterized in that its flexural modulus at room temperature is at least 3000 N/mm.sup.2 and that its falling dart energy at break, at -30.degree. C., is at least 40.0 J. Sheets extruded of the composition are suitable for making useful articles by thermoforming.