Abstract The development of eco-friendly composites as insulating materials in buildings offers practical solutions to reduce energy consumption, which is why scientists have started in recent decades to search for more sustainable and eco-friendly materials. It is well known that building materials are among the most commonly used materials and have an obvious negative impact on the environment. Therefore, this article presents a study on the use of a new bio-composite material, composed of natural fibers of date palm, cement, and sand. The objective of this study is to assess the thermal insulation properties, as well as the water absorption and mechanical performance of this material for the construction of buildings. The percentage by weight of date palm fiber in the test samples varied from 0% to 30% for a mixture of two fiber sizes equal to 3 mm and 7 mm. The characteristics of these samples were determined experimentally in terms of compressive strength, as well as thermal conductivity. The results show that the introduction of date palm fibers in mortars causes a decrease in compressive strength and thermal conductivity. This study affirmed that the use of vegetable fibers in cementitious composites has a positive effect on the properties of insulations and on the costs.