Abstract Application of thermal energy storage technology in practical engineering has been inhibited due to the constant strong rigidity of phase change materials (PCMs) at any given temperature. To solve this problem, a novel kind of thermal sensitive flexible PCMs was developed by using difunctional olefin blockcopolymer (OBC) replacing conventional supporting materials. Due to phase separation morphology, OBC presents physical crosslinked network and elasticity which is essential for macroscopical elastic deformation of composite. The developed PCMs based on OBC not only exhibit the same high latent capacity and stable shape as shape-stabilized PCMs, but also present thermal sensitive flexibility with the melting point of paraffin T paraffin,m as the stimulus. Below the melting point of OBC- T OBC,m , the transformation from rigid to flexibility is reversible. The above excellent flexibility of the developed PCMs contributes to reducing thermal contact resistance and improving poor installation for conventional PCMs in energy storage field, such as in energy-storage air-conditioning and compact electron device thermal control, especially in spacecraft thermal control system. Furthermore, thermal conductivity was improved to a breakthrough level (479% of original rate) by adding 3 wt.% of the maximum size of expanded graphite, which is based on the guidance of the novel calculation model on account of thermal conductivity for thermal sensitive flexible PCMs.