The present invention relates to a curable isocyanate-free formulation for preparing a polyurethane self-blowing foam comprising at least one multifunctional cyclic carbonate having at least two cyclic carbonate groups at the end of the chain (compound A), at least one multifunctional amine (compound B), at least one masked thiol precursor (compound C) and optionally at least one catalyst (compound D), to a process for preparing said foams, to the thus obtained foams and to the recycling of said foams.