Abstract: A thermal energy storage medium comprising a hydrophilic polysaccharide supporting an inorganic salt that is capable of transforming from one phase to a less hydrated phase absorbing latent heat, and releasing this latent heat upon the reverse transformation. The polysaccharide, preferably Xanthan Gum, may be incorporated in concentrations of 0.05% to 3% together with a nucleating agent in order to form a material that transforms when cooled back to the transformation temperature, or in greater concentrations of 1% to 5% without a nucleating agent to form a material that may be cooled below the transformation temperature without transformation taking place, and stored at ambient temperature while still storing the latent heat until activated.The medium is gelled in the less hydrated phase and in some embodiments the gel is pseudoplastic thus enabling it to be poured into chambers of an energy storage device, and then regain its original viscosity at rest.