High‐performance binary blends between poly(ether imide) (PEI) and flame‐retardant poly(butylene terephthalate) (PBT) are modified with 5, 10, and 15 wt% of poly(tetrafluoroethylene) (PTFE) using a two‐step melt‐processing method. Morphology study reveals that PTFE does not interfere with PEI and PBT interfacial interaction during blends fabrication, and the dual‐phase inversion observed for binary PEI/PBT blends in previous works remains the same. Thermal degradation and fire resistance analyses show that charring layer formation is the major flame protection process and that PTFE enhances charring production for ternary blends. According to UL94 horizontal burning test, all blends are categorized as slow‐burning materials. Bomb calorimetry and thermal gravimetric analyses reveal that there is an interaction between PTFE with PEI and PBT phases, as well as with their degradation products. This phenomenon is explained by X‐ray photoelectron spectroscopy analysis, and it is attributable to Sb‐F species which enhances the formation of an intumescent layer.