was developed in two steps: the first one focused on the effects of different fine aggregates and admixtures for a fixed PCM content and the second one on the effect of changing the amount of PCM. Results show that using silica aggregates and antifoaming admixture outperform the other options, producing mortars with statistically significant higher thermal conductivities, diffusivities and effusivities. Besides, increasing the amount of PCM significantly reduces conductivity and diffusivity, but the effusivity is practically invariant. This suggests that the mortar design has to be defined by predominantly focusing on diffusivity, in order to achieve appropriate heat penetration rates and activation times for an efficient system operation.