ABSTRACTOn the basis of ammonium polyphosphate (APP) microencapsulated with pentaerythritol/dibromoneopentyl glycol (DBNPG) mixed phosphate melamine salt as an intumescent flame retardant (IFR), the influence of DBNPG on the flame retardancy of IFR/low‐density polyethylene was investigated. The results prove that DBNPG could influence the combustion heat and the thermal barrier properties of the char layer in combustion. The intumescent degree (ID), compactness, and closure were the determinants of the thermal barrier properties of the char layer. A greater ID below 500°C and then a more compact and closed char layer above 500°C contributed to the better thermal barrier properties. An appropriate DBNPG reduced the combustion heat and promoted the formation of a compact and closed char layer by increasing of the melting viscosity of the composites. However, excessive DBNPG destroyed the closure of the char layer and increased the combustion heat because of a decrease in the melting viscosity of the composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2015,132, 41244.