Featured Application: This work faces applications in energy-saving buildings. The involved shape-stabilized phase change material is a promising material used in walls or floors of buildings to regulating the room temperature in a comfortable range, taking advantage of clean and sustainable solar energy or off-peak electricity. Abstract:The thermal conductivity of expanded graphite plate (EGP) and/or multi-wall carbon nanotube (MWCNT)-filled, shape-stabilized, phase change material (SSPCM), based on paraffin, high-density polyethylene (HDPE), and styrene-butadiene-styrene copolymer (SBS), was investigated. The results demonstrated that both EGP and MWCNT increased the thermal conductivity of the SSPCM. EGP showed a greater thermal conductivity improvement than MWCNT. The conductivity of EGP-filled SSPCM reached 0.574 W/mK at 9 wt %, while that of MWCNT was just 0.372 W/mK at the same loading. Furthermore a series of EGP/MWCNT hybrid fillers were prepared and introduced into the SSPCM, and a synergistic effect was observed between the two fillers. When the EGP/MWCNT ratio was 8:2, the most significant thermal conductivity enhancement to the SSPCM was obtained. The thermal conductivity was 0.674 W/mK, 288% that of the SSPCM and 117% that of 9 wt % EGP-filled SSPCM. The SEM photos showed that a bridging of two-dimensional (2D) planar EGP by flexible one-dimensional (1D) MWCNT was constructed. The so-formed EGP-MWCNT network favored heat transfer along it and led to a decreased thermal interface resistance due to the increased EGP-MWCNT junctions.