The flammabilities of a series of polyesters, varying both the diol length and the degree of aromaticity of the diacid units were evaluated using cone calorimetry. Addition of inorganic additives, copolymerization with sulfoisophthalate ionomeric units and with the phosphorous flame retarding agent, phospholane, were also examined. A strong, linear relationship between the polymer carbon:hydrogen ratio and various flammability indicators was established. The phospholane was demonstrated to produce only a modest reduction in flammability, whereas the isomeric comonomer produced an unexpectedly strong reduction in all aspects of flammability tested. Addition of inorganic modifiers resulted in varied, and relatively modest changes in polyester flammability. (C) 2014 Elsevier Ltd. All rights reserved.