The present invention relates to an impregnation process for a functional fibrous substrate, a liquid composition for implementing this process and the obtained impregnated fibrous substrate. The impregnated functional fibrous substrate is suitable for manufacturing mechanical or structured parts or articles. In particular the present invention deals with an industrial process for impregnating a functional fibrous substrate or long functional fibers with a viscous liquid composition containing mainly monomer components. This viscous composition is called hereafter liquid monomer syrup. The invention concerns also a functional fibrous substrate pre-impregnated with said syrup which is useful for manufacturing mechanical or structured parts or articles. More particular the impregnation of functional fibrous substrate with the monomer syrup is achieved in a mould. The present invention concerns also manufacturing process for manufacturing mechanical or structured parts or articles and three-dimensional mechanical or structured parts obtained by this process.