Carbon foams specifically designed for seasonal solar thermal energy storage (SSTES) were prepared and characterised. For working efficiently as hosts for sugar alcohols used as phase-change materials and allowing the achievement of compact and affordable systems for SSTES, drastic conditions were required: thermal conductivity higher than 3 W m−1 K−1, porosity higher than 86% and cost not much higher than 6 € kg−1. For designing such materials, carbon foams combining a partly graphitised matrix derived from sucrose char, filled by natural graphite flakes of typical size 6 μm were suggested. Nickel nitrate was used as both graphitisation catalyst and blowing agent. Both nitrate and graphite were selected out of other materials of the same kind, shown to present lower performances. As thermal conductivity and porosity vary in opposite ways, finding a formulation optimising both parameters was only possible through an experimental design associated with statistical analysis of results. The results were modelled, and the model allowed finding formulations matching all initial requirements. Such good results were explained by the excellent dispersion of graphite filler and partial graphitisation of the matrix evidenced by polarised-light optical microscopy, X-ray diffraction and Raman mapping studies. Display omitted