Hexafluorophosphoric acid refers to a family of salts produced by combining phosphorus pentafluoride and hydrofluoric acid. The idealized chemical formula for hexafluorophosphoric acid is HPF6, which also is written H[PF6]. Hexafluorophosphoric acid is only stable in solution, decomposing to HF and PF5 when dry. It exothermically reacts with water to produce oxonium hexafluorophosphate ([H3O]+[PF6]−) and hydrofluoric acid. Additionally, such solutions often contain products derived from hydrolysis of the P-F bonds, including HPO2F2, H2PO3F, and H3PO4, and their conjugate bases. Hexafluorophosphoric acid attacks glass. Upon heating, it decomposes to generate HF. Crystalline HPF6 has been obtained as the hexahydrate, wherein PF−6 is enclosed in truncated octahedral cages defined by the water and protons. NMR spectroscopy indicates that solutions derived from this hexahydrate contain significant amounts of HF.