Disclosed is a flame-retardant composition comprising (i) 40-66 wt. % alkenyl aromatic resin, (ii) 9-33 wt. % ammonium polyphosphate and (iii) 14-40 wt. % cellulosic material, wherein all weights are based on the total weight of the composition and wherein ammonium polyphosphate and cellulosic material are present in a weight % ratio effective to provide molded articles exhibiting at least V-1 flame rating as determined according to the UL-94 protocol. A process to prepare the composition and articles comprising a composition of the invention and/or made by the process of the invention described herein are also disclosed.