Polyolefins are used in a plethora of application fields: building, automotive, railways, E&E… Those fields are concerned by fire regulations and the inherent flammability of polyolefins can be the source of fire hazards. Intumescence was selected to provide polyolefins with flame retardancy. The intumescence process results from a combination of charring and foaming at the surface of the substrate. The intumescent coating expands and forms an insulative layer at the surface of the substrate upon heating. The charred layer acts as a physical barrier, which slows down heat and mass transfer between gas and condensed phase. The formation of an intumescent char is a complicated process involving several critical aspects: rheology (expansion phase, viscoelasticity of char), chemistry (charring) and thermophysics (limitation of heat and mass transfer). The purpose of the talk is to develop new formulations for polyolefins (in particular polypropylene (PP) and ethylene-vinyl acetate copolymer (EVA)). The concept is to use additional ingredients in basic intumescent formulation to create synergistic effect. It is shown zinc carbonate can reduce significantly peak of heat release rate (pHRR) in intumescent EVA. In order to investigate the mechanism of action, the tests are instrumented (thermocouples in the samples, IR thermography …) to get information on the fire behavior of the samples. Advanced analyses (MTGA, kinetic analysis, solid state NMR, X-ray tomography …) are also employed. Finally, new intumescent formulations are suggested to optimize FR performance in polyolefins.