Abstract: An auto-expansible cushioning bag constituted by a completely closed envelope of flexible, impervious and transparent material, and by at least two hermetically closed sachets, likewise of flexible, transparent and impervious material, which are integrated into the envelope and contain the ingredients necessary for the production of a foam of polyurethane or the like. The one sachet contains a mixture of polypropylene glycol ("polyol"), activators, water from which CO.sub.2 gas is generated to cause the expansion, and possibly a supplementary inflating agent, such as trichlorofluoromethane, and the other contains an isocyanate.