Abstract For the storage of latent thermal energy (LTES), phase change materials (PCM) are the most commonly used. Nonetheless, their low thermal conductivity values and the liquid leakage on the transition phase of process limits their application. Hence, the stabilization-form can be a solution to surmount these two limitations. In this work, the Hexadecane with large latent heat was used as PCM, styrene-b-(ethylene-co-butylene)-b-styrene (SEBS) tri-block copolymer and the low-density polyethylene (LDPE) served as the supporting materials and expanded graphite (EG) was added for improving the thermal conductivity. We focused on the preparation of SEBS/Hexadecane/LDPE Composites and the improvement of the heat transfer using the EG. The Fourier Transformation Infrared spectroscope also demonstrated a good compatibility between SEBS, LDPE, Hexadecane, and EG. The transient Guarded Hot Plate Technique (TGHPT) and a Thermogravimetric analyzer were utilized to assess the thermal properties and thermal stability of the PCM composites respectively. Further, a leakage test proved that the composite has an excellent form-stable property. Thanks to expanded graphite, no hexadecane leakage was depicted at a 75% mass fraction of PCM in composites, which surmounts almost all mass fraction values reported in the literature.