Water is an inorganic, non-flammable and easily available phase change material (PCM), which can be utilized for cold thermal energy storage (TES) application (melting point at 0$^{\circ}$C). Although water has a specific heat ofabout 4.18 J g$^{–1}$ K$^{–1}$ and has melting enthalpy of about 333 J g$^{–1}$, its application as an insulation layer was constrained. Phase separation (bulk convective movement during phase change, between ice and water), leakage from the container, supercooling during freezing, volumetric expansion and corrosion to the container were the main concerns for water as an insulation layer in TES systems. In this study, a thick non-flowing hydrogel (shape-stabilized PCM) was prepared by adding a small amount of inorganic additive material called LAPONITE$^{\circledR}$in water. The idea is to propose this thick nonflowing hydrogel as an insulating layer for cold TES application. The effect of this additive on viscosity and thermal properties of the water was studied. The phase change phenomenon of this hydrogel (between –10 and 20$^{\circ}$C) was compared with water and the results are discussed.