HOFs are a sub-class of porous solids whose structures are driven by hydrogen bonding, which is typically weaker than the directional coordination bonding in MOFs. Hence, assumptions about crystal packing based on intuitive 'rules' are more prone to fail. For example, even though the hydrogen bonding in the benzimidazalone molecules that we studied is particularly strong and directional, there are at least four competing porous polymorphs that are all defined by 1-dimensional hydrogen-bonded tapes. There is no single dominant porous form, and although all four porous polymorphs can be predicted as low-energy structures, the specific polymorph that is produced by experiment is influenced by the choice of crystallization solvent.