Coaxial electrospinning of poly(ethylene glycol) (PEG)/polyamide 6 (PA6) was successfully used in development of nanofibrous thermal energy storage (TES) material. Halloysite nanotubes (HNTs) were introduced into the core/shell structured TES materials at various concentrations (0.5, 1, 3 and 5 wt. %). Surface activation of HNT was also conducted by piranha etching in order to increase the affinity between piranha-etched nanotubes (HNT-P) and PEG. The core/shell structured materials were characterized using SEM, FTIR, TGA, DSC, tensile and thermal cyclic tests. With incorporation of 3 wt. % HNT-P into the core/shell nanofibers, tensile modulus and latent heat of melting values were increased by 25 % and 21 %, respectively. Additionally, PEG encapsulation efficiency of the neat core/shell nanofibers was increased from 78 % to 96 % with 3 wt. % HNT-P addition. The neat core/shell samples preserved 88 %, whereas 3 wt. % HNT and HNT-P added nanofibrous samples preserved 94 % of their initial melting enthalpies.