Fibrids of polyolefins showing a high degree of fibrillation and a high specific surface area are obtained by flashing a pressurized solution of polyolefin in pentane or in a pentane-containing solvent mixture at a temperature above the boiling point of the solvent by passing said solution through an orifice into a space which is at a lower pressure and in which shearing forces are applied to said solution. The fibrids directly obtained may be used, for example, for the manufacture of paper or for the manufacture of textile-like webs.