The present work is a part of a large project aimed at design and development of new composite materials containing date palm fibers (DPF) primarily suitable for thermal insulation in various sectors, especially in the building sector. On one hand, porosity (P) and Young's modulus (E) of gypsum based composites reinforced with DPF were investigated. On other hand, thermal resistance and time lag of composites were also studied. The results showed that E of DPF reinforced gypsum materials is mainly affected by the interfacial adhesion between matrix and DPF. The effect of DPF sizes and loadings is highly significant on the stiffness of gypsum. It's noted that the adding of DPF on gypsum induces an increase of both time lag and thermal resistance of composites. This new biocomposite can be used as a raw material for reinforcement gypsum materials in order to produce a friendly biocomposite materials to use for thermal insulation in buildings. (C) 2016 Elsevier B.V. All rights reserved.