Polymorphism in hexanitrohexaazaisowurtzitane crystallized from solution

► Crystallization behavior of HNIW polymorphs obey by Ostwald's rule of stages. ► Form β is preferentially initial precipitate in polar anti-solvent, and then transform to form ε. ► Hydrate formation and stability are related to the content of water in solution. ► A new solvate precipitates from acetone solution was found. ► Form γ precipitates at high temperature affected by the nature of solvent.