This paper presents an investigation on the use of a new material, composed with natural cement, sandand date palm fibers (DPF). The main goal is to evaluate the possibility of using this new material as insu-lating building materials. Several composites were prepared for different weight concentrations (from0% to 30%) and for three sizes of fibers. Water absorption, thermal conductivity and compressive strengthwere experimentally investigated. The results reveal that the incorporation of DPF reduces the thermalconductivity and the compressive strength of the composite while reducing the weight. For a DPF load-ing lower than 15%, the composite satisfies both thermal and mechanical requirements of constructionmaterials, and they could be used for wall structures. Thus, utilization of DPF as filler in mortar seems tobe a very promising option which allows to be applied as thermal insulation materials in buildings.