Manufacture of a pre-impregnated fibrous material which contains continuous fibers and a thermoplastic matrix, the material being made as a plurality of unidirectional parallel ribbons or sheets, and the method involving a step of pre-impregnating, in dry conditions, N parallel strands divided into X groups of Ni strands, by the thermoplastic matrix in powder form in a tank, ΣNi=N et X 3, one thereof from each series being immersed in the powder, each group of strands running on the same number Y of tensioning parts, and the parallel strands being separated by a spacing at least equal to the width of each strand.