The phase change materials (PCM) are known since years with high thermal storage capacity but with limited applications. The modified PCM mainly paraffin watery suspensions, so called PCM slurry, improve some PCM drawbacks (thermal conductivity) and as paraffin multifunctional fluids can work in both, heat transport and heat storage for cooling technology applications. The structural and thermophysical properties of two types PCM slurry were good basis for comparison of their efficiency: paraffin microcapsule slurry (A) and paraffin emulsion slurry (B), both working in temperature range of phase transition from 2-12 degreesC. The equipments as differential scanning calorimetry (DSC), model NETZSCH DSC 200 PC; scanning electron microscopy (SEM), JOEL model JSM-5510; hot stage optical microscopy, LINKAM model TMS 94 and hand made thermal cycling system operational with Danfoss cooling machine that ensured 2 kW cooling capacity at 40oC; gave accurate results, characterizing completely, from structural and thermal point of view both types of PCM multifunctional structured fluids. Structural stability of the advanced phase change multifunctional fluids was discussed on sample imaging in variable magnifications made by method of Hot Stage microscopy and precise SEM study. Systematization of the DSC results obtained, including temperature range of phase transition and thermal storage capacity, measured before and after repeatable thermal cycling of the PCM multifunctional fluids, allowed selection of the PCM slurry working samples with relatively high thermal capacity applicable to further development in prototypes. Heat absorbed/released, calculated by NETZSCH DSC software, was for PCM slurry A in the range of 80 to 82 kJ/kg, while PCM slurry B showed thermal storage capacity from 56 to 53 kJ/kg. Correlation between the structural properties and thermal storage capacity of the phase change multifunctional fluids led to practical conclusions concerning: homogeneity; crystal growth/conditions; structural compatibility between components; prediction of the heat flow behavior of multifunctional PCM slurries in cooling technology for storage and transport of heat.