Polypropylene, polylactide, and chitosan were filled with lignocellulosic flax fibers, micrometric cellulose, and nanometric cellulose. The fillers were subjected to phys. or/and chem. modifications. A hybrid filler was also prepd. by mixing nanometric cellulose with montmorillonite and used for reinforcing chitosan. The filling resulted in increasing Young modulus and tensile strength and in decreasing the elongation at break except for polylactide where the tensile strength decreased after filling.