▎ 摘　　要

The potential safety hazard associated to commonly used flame retardant chemicals generates a strong demand for new, sustainable, and high performing solutions to reduce the fire threats of widespread polymer foams. In this work, the production of self-extinguishing, nonignitable, and flame resistant flexible polyurethane foams by means of simple layer-by-layer assembly of graphene oxide nanoplatelets is reported. The process builds a protective exoskeleton that completely wraps the complex 3D structure of the foam and is capable of stopping flame spread in flammability tests and preventing ignition when exposed to heat fluxes typical of developing fires. In addition, treated foams are found able to withstand the penetration of a flame torch, successfully protecting the unexposed side from thermal decomposition for more than 6 min. The outstanding temperature gradient greater than 500 degrees C cm(-1) achieved through the foam thickness makes the performances of these foams comparable to those of a silica aerogel, while maintaining excellent flexibility and toughness. The results reported in this paper represent a tremendous opportunity for the production of a novel class of organic and flexible foams, capable of ensuring unprecedented fire safety properties while relying on an easy, green, and straightforward approach to material design.