There is a great need to develop new polymer foam systems that combine the advantages of polyurethane foams (low cost, ease of processing, desirable physical properties) with nonflammability and thermal stability which polyurethanes lack. In this project we address this need by synthesizing novel polymer networks with a substantial content of nonflammable elements. Specifically most of the pendant hydrogens have been eliminated (or replaced with fluorine), and a substantial fraction of the carbon atoms are replaced with oxygen, phosphorus, and nitrogen. Other elements such as Ca, Mg, Al, Sb, V, and B are also incorporated in the polymer network to enhance nonflammability. The selected phosphorus compounds are in their highest oxidation state (+5) and the nitrogen is present in the form of five or six-member heterocyclic rings. Following these guidelines, several rigid, semi-rigid, and flexible, foamed-in-place foams with outstanding nonflammability and thermal stability have been developed.