The present invention relates to a process for the elongation and/or densification of fibers, on a keratin material, characterized in that it employs a composition, especially a cosmetic composition, in particular a makeup composition, comprising at least: —one volatile hydrocarbon-based oil, —particles of at least one polymer surface-stabilized with a stabilizer, and —a hydrophobic film-forming polymer, chosen from hydrocarbon-based block copolymers, hydrocarbon-based resins, and mixtures thereof.