The invention relates to the use of isotactic polypropylenes of very great fluidity for the preparation of concentrates of fillers which can be used in thermoplastics of the olefinic type such as polypropylene, polyethylene and as a general rule: the polymers used alone or in a mixture, based on ethylenic monomers containing 2 to 6 atoms of carbon polymerized alone or in a mixture. The invention also relates to the concentrates of fillers or master batches prepared from isotactic polypropylenes of very great fluidity. The invention finally relates to the loaded thermoplastic materials obtained with the addition of selected polypropylenes according to the invention, and the industrial products manufactured from, or containing, such thermoplastic materials.