In this Application Note sodium chloride (NaCl) and mannitol are used for freeze drying experiments. The unambiguous crystal structure of NaCl renders this salt a model compound. In contrast, mannitol is well known to crystallize in different polymorphs and it may form hydrates. Nevertheless, mannitol is the most used bulking agent for freeze dried pharmaceutical formulations. The benefits of using mannitol are that it crystallizes during freezing, creates a beautiful cake and permits drying processes at higher product temperatures, thus with higher sublimation rates compared to purely amorphous systems.