The aim in this paper is the presentation of the influence of modification of polypropylene (PP) fibres on sorption capabilities of fibres. Modification of PP fibres were made with inorganic additives in the mass with a view to improving silicate composites – in construction. The prepared modified PP fibres were compared with pure PP fibres and their mechanical and thermomechanical properties were evaluated. And we wanted to evaluate and compare the sorption capabilities of these fibres using the Washburn method. However, the obtained results led us to the conclusion that the given method rather points to the excellent transport properties of PP fibres, as if it evaluated the sorption of the fibres.