NOVELTY - Preparing a prepreg fiber material in ribbon form, containing a fibrous reinforcement and a thermoplastic polymer matrix, comprises (a1) impregnating a fibrous material in the form of a single wick or multiple parallel wicks by a polymer melt, in which the polymer melt during the impregnation contains a neutral gas, preferably supercritical carbon dioxide in the supercritical state, used as an agent to aid the implementation by reduction in viscosity in the molten state.    USE - The method is useful for preparing a prepreg fiber material, in ribbon form, which is useful: for making suitable calibrated ribbons in making three-dimensional composite parts by automatically depositing the ribbons by robot, where the three-dimensional composite parts are related to automobiles, civil or military aerospace, wind energy, tidal energy, energy storage devices, thermal protection panels, solar panels, ballistics weapons or missiles, security, nautical, sports and recreation, building and construction, or electronics; and in three-dimensional composite member (all claimed).    ADVANTAGE - The method provides: the prepreg fiber material having a homogeneous impregnation of the fibers and with a porosity and controlled and reproducible dimensions; and good quality composite materials.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) the prepreg material, in the form of ribbon, preferably wrapped on coil (101), comprising a pre-impregnated fibrous material obtained by the above method; and    (2) an implementation unit (200) for preparing the prepreg fiber material, in ribbon form, comprising: a continuous impregnation device (40) with a single wick or many parallel wicks of fibrous material comprising an impregnating die fed by polymer melt containing the neutral gas in the supercritical state; and a continuous calendering device of single wick or parallel strands, with formatting, in the form of unidirectional single ribbon or unidirectional multiple parallel ribbons, comprising (a) at least one heating calender (60), preferably many heating calenders in series, and (b) a servo control system of the pressure and/or the spacing between the calendering rolls, where the calender comprises a calendering groove or multiple calendering grooves, preferably up to 200 calendering grooves.    DESCRIPTION OF DRAWING(S) - The figure shows a side view of an implementation unit.    Impregnation device (40)    Heating calender (60)    Coil (101)    Implementation unit (200)    Rollers (601)