Nowadays, in the purpose of energy saving and eco-friendly technologies and materials, increasing interest is accorded to natural vegetable fibers. Many studies have shown that vegetable fibers are an alternative to asbestos in fiber reinforced cement products manufacturated by the Hatscheck process. Few works have demonstrated the low thermal conductivity of such composite materials resulting from effect of the mixture fiber/matrix. The aim of this study is to produce low–cost building materials in the purpose of saving energy using heat-treated and chemically treated sugar cane bagasse and fique fibers as reinforcement in cement (OPC) based materials. Consequently, the influence of the type and weight of additives on the insulating thermal properties (conductivity) and on the mechanical properties (flexural strength) are prospected. This study evidences that composites composed with pyrolyzed bagasse fibers have better thermal properties than others composites. The higher mechanical properties are noted for composites manufactured with alkali treated fibers.