A versatile system to construct bulk polymeric phononic crystals by using acoustic waves is described. In order to fabricate this material, a customised cavity device fitted with a ∼2 MHz acoustic transducer and an acoustic reflector is employed for the acoustic standing wave creation in the device chamber. The polymer crystal is formed when the standing waves are created during the polymerisation process. The resulting crystals are reproduced into the shape of the tunable device cavity with a unique periodic feature. The separation is related to the applied acoustic wave frequency during the fabrication process and each unit cell composition was found to be made up to two material phases. To assess the acoustic properties of the polymer crystals their average acoustic velocity is measured relative to monomer solutions of different concentrations. It is demonstrated that one of the signature characteristics of phononic crystal, the slow wave effect, was expressed by this polymer. Furthermore the thickness of a unit cell is analysed from images obtained with microscope. By knowing the thickness the average acoustic velocity is calculated to be 1538 m/s when the monomer/cross-linker concentration is 1.5 M. This numerical calculation closely agrees with the predicted value for this monomer/cross-linker concentration of 1536 m/s. This work provides a methodology for rapid accessing a new type of adaptable phononic crystal based on flexible polymers.