Abstract: 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. BF4—). 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.