Zeolites are known to be one of the few classes of materials that can feature negative thermal expansion (NTE), where the material contracts upon heating, a difference from most materials which expand upon heating. In zeolites, as in some other framework materials, the NTE behaviour has been attributed to the presence of Rigid Unit Modes (RUMs) originating from their corner-sharing tetrahedral structure. When heated, these RUMs permit the 'flexing' or rotation of these tetrahedral units within the zeolitic framework, causing an overall contraction of the material -thus leading to NTE. Essentially, the thermal energy allows the rotation of the corner-sharing tetrahedra, resulting in a smaller overall volume even as temperature rises. Both experimental and in-silico investigations found exceptions to this behaviour, i.e., zeolites with positive thermal expansions (PTE), but since their rarity and the presence of RUMs in all of these frameworks, is still debate that PTE in these systems is due to the nano-porous nature of the material instead of the framework itself.