Flame retardancy of flexible polyurethane foams: traditional approaches versus layer-bylayer assemblies

This chapter provides an overview of the flame retardancy of flexible polyurethane foams. In particular, the different chemical structures of polyurethanes are discussed, underlining the most relevant aspects related to thermal decomposition and combustion. A brief description of the toxicity of the combustion gases is provided. The traditional strategies developed in the past are presented and commented upon, highlighting the main results achieved. Subsequently, layer by layer is discussed as new emerging approach for conferring flame-retardant properties to open-cell polyurethane foam. The principles of this technique and its practical applications in flame retardancy are presented, providing a complete overview of the results achieved so far. Finally, there is a discussion on the future perspectives and unmatched needs, and a comparison between old and new approaches.