Flexible polyurethane foams (FPUF) are commercially used cushioning materials, but severely suffer from fire risks due to their inherent flammability. Surface coating can localize flame-retardant functionality at the polymer-air interface without altering bulk properties. However, developing a facile nanocoating strategy beyond the layer-by-layer technique for FPUF remains challenging. This work reports novel flame-retardant FPUF@PMo-PPy composites, fabricated by uniformly depositing phosphomolybdic acid (H₃PMo₁₂O₄₀, PMo₁₂) clusters encapsulated within polypyrrole (PPy) via in situ polymerization onto the FPUF skeleton surface, based on electrostatic interactions. The PMo-PPy coating significantly mitigates the fire hazards of FPUF, exhibiting a maximum reduction of 66.7% in peak heat release rate (pHRR) and 73.5% in peak smoke production rate (pSPR). Notably, the maximum smoke density (D_max) and smoke density at 10 min (D_{10 min}) were reduced by 55.7% and 60.8%, respectively, accompanied by lower pyrolysis gas toxicity (HCN and CO). This enhancement is attributed to decomposition products—phosphoric acid and MoO₃—generated from the PMo-PPy coating, which improve the stability and compactness of the char layer. This PMo-PPy nanocoating strategy provides a security assurance for cushioning materials in industrial engineering, ensuring the security of life and property.