With　the　advantages　of　lightweight　and　low　thermal　conductivity　properties,　polymeric　foams　are　widely　employed　as　thermal　insulation　materials　for　energy-saving　buildings　but　suffer　from　inherent　flammability.　Flame-retardant　coatings　hold　great　promise　for　improving　the　fire　safety　of　these　foams　without　deteriorating　the　mechanical-physical　properties　of　the　foam.　In　this　work,　four　kinds　of　sulfur-based　flame-retardant　copolymers　are　synthesized　via　a　facile　radical　copolymerization.　The　sulfur-containing　monomers　serve　as　flame-retardant　agents　including　vinyl　sulfonic　acid　sodium　(SPS),　ethylene　sulfonic　acid　sodium　(VS),　and　sodium　p-styrene　sulfonate　(VSS).　Additionally,　2-hydroxyethyl　acrylate　(HEA)　and　4-hydroxybutyl　acrylate　are　employed　to　enable　a　strong　interface　adhesion　with　polymeric　foams　through　interfacial　H-bonding.　By　using　as-synthesized　waterborne　flame-retardant　polymeric　coating　with　a　thickness　of　600 µm,　the　coated　polyurethane　foam　(PUF)　can　achieve　a　desired　V-0　rating　during　the　vertical　burning　test　with　a　high　limiting　oxygen　index　(LOI)　of　＞31.5 vol%.　By　comparing　these　sulfur-containing　polymeric　fire-retardant　coatings,　poly(VS-co-HEA)　coated　PUF　demonstrates　the　best　interface　adhesion　capability　and　flame-retardant　performance,　with　the　lowest　peak　heat　release　rate　of　166 kW　m−2　and　the　highest　LOI　of　36.4 vol%.　This　work　provides　new　avenues　for　the　design　and　performance　optimization　of　advanced　fire-retardant　polymeric　coatings.　©　2024　The　Authors.　Macromolecular　Rapid　Communications　published　by　Wiley-VCH　GmbH.