There is herein described phase change materials (PCMs) comprising at least one or a plurality (e.g. a mixture) of tetrafluoroborate salts that are capable of undergoing a solid to solid phase transition. In particular, there is described phase change materials (PCMs) comprising at least one or a plurality (e.g. a mixture) of tetrafluoroborate salts where there is at least one tetrafluoroborate salt or a plurality of tetrafluoroborate salt which have a solid to solid phase transition. The tetrafluoroborate salt may comprise at least one anion or a plurality of the same or different anions of tetrafluoroborate (e.g. BF 4 -). The PCM may have a solid to solid phase change in the region of about -270°C to about 3,000°C, about -50°C to about 1,500°C, about 0°C to about 1,000°C, or about 0°C to about 500°C temperature range.